Science.gov

Sample records for dacs-sc dendreon buoyant

  1. Sipuleucel-T: APC 8015, APC-8015, prostate cancer vaccine--Dendreon.

    PubMed

    2006-01-01

    Sipuleucel-T [APC 8015, Provenge] is an autologous, dendritic cell-based vaccine under development with Dendreon Corporation for the treatment of androgen-independent and androgen-dependent prostate cancer. It was generated using the company's active immunotherapy platform to stimulate a patient's own immune system to specifically target and destroy cancer cells, while leaving healthy cells unharmed. This approach could provide patients with a meaningful survival benefit and an improved tolerability profile over existing anticancer therapies. Sipuleucel-T selectively targets the prostate-specific antigen (PSA) known as prostatic acid phosphatase (PAP) that is expressed in approximately 95% of prostate cancers. It is produced by ex vivo exposure of dendritic cell precursors to PA 2024, a recombinant fusion protein composed of the PAP target fused to granulocyte-macrophage colony-stimulating factor (GM-CSF) and incorporated into Dendreon's proprietary Antigen Delivery Cassette. Patients are typically administered three intravenous (IV)-infusions of the vaccine over a 1-month period as a complete course of therapy. It is undergoing late-stage clinical evaluation among patients with early and advanced prostate cancer. In November 2003, Kirin Brewery returned to Dendreon the full rights to Sipuleucel-T for Asia. In exchange, Dendreon licensed patent rights relating to the use of certain HLA-DR antibodies to Kirin for $US20 million. This amended agreement enables Dendreon to complete ongoing discussions for a worldwide marketing and sales partnership for Sipuleucel-T. Similarly, Kirin is able to develop its HLA-DR monoclonal antibodies free of potential infringement claims arising from Dendreon's patent rights to HLA-DR. The licensing agreement relates to patent rights owned by Dendreon relating to monoclonal antibodies against the HLA-DR antigen. In addition, Dendreon retains rights to develop and commercialise its two existing HLA-DR monoclonal antibodies, DN 1921 and

  2. Hydrostatic Modeling of Buoyant Plumes

    NASA Astrophysics Data System (ADS)

    Stroman, A.; Dewar, W. K.; Wienders, N.; Deremble, B.

    2014-12-01

    The Deepwater Horizon oil spill in the Gulf of Mexico has led to increased interest in understanding point source convection dynamics. Most of the existing oil plume models use a Lagrangian based approach, which computes integral measures such as plume centerline trajectory and plume radius. However, this approach doesn't account for feedbacks of the buoyant plume on the ambient environment. Instead, we employ an Eulerian based approach to acquire a better understanding of the dynamics of buoyant plumes. We have performed a series of hydrostatic modeling simulations using the MITgcm. Our results show that there is a dynamical response caused by the presence of the buoyant plume, in that there is a modification of the background flow. We find that the buoyant plume becomes baroclinically unstable and sheds eddies at the neutral buoyancy layer. We also explore different scenarios to determine the effect of the buoyancy source and the temperature stratification on the evolution of buoyant plumes.

  3. Buoyant plume calculations

    SciTech Connect

    Penner, J.E.; Haselman, L.C.; Edwards, L.L.

    1985-01-01

    Smoke from raging fires produced in the aftermath of a major nuclear exchange has been predicted to cause large decreases in surface temperatures. However, the extent of the decrease and even the sign of the temperature change, depend on how the smoke is distributed with altitude. We present a model capable of evaluating the initial distribution of lofted smoke above a massive fire. Calculations are shown for a two-dimensional slab version of the model and a full three-dimensional version. The model has been evaluated by simulating smoke heights for the Hamburg firestorm of 1943 and a smaller scale oil fire which occurred in Long Beach in 1958. Our plume heights for these fires are compared to those predicted by the classical Morton-Taylor-Turner theory for weakly buoyant plumes. We consider the effect of the added buoyancy caused by condensation of water-laden ground level air being carried to high altitude with the convection column as well as the effects of background wind on the calculated smoke plume heights for several fire intensities. We find that the rise height of the plume depends on the assumed background atmospheric conditions as well as the fire intensity. Little smoke is injected into the stratosphere unless the fire is unusually intense, or atmospheric conditions are more unstable than we have assumed. For intense fires significant amounts of water vapor are condensed raising the possibility of early scavenging of smoke particles by precipitation. 26 references, 11 figures.

  4. Buoyant Norbury's vortex rings

    NASA Astrophysics Data System (ADS)

    Blyth, Mark; Rodriguez-Rodriguez, Javier; Salman, Hayder

    2014-11-01

    Norbury's vortices are a one-parameter family of axisymmetric vortex rings that are exact solutions to the Euler equations. Due to their relative simplicity, they are extensively used to model the behavior of real vortex rings found in experiments and in Nature. In this work, we extend the original formulation of the problem to include buoyancy effects for the case where the fluid that lies within the vortex has a different density to that of the ambient. In this modified formulation, buoyancy effects enter the problem through the baroclinic term of the vorticity equation. This permits an efficient numerical solution of the governing equation of motion in terms of a vortex contour method that tracks the evolution of the boundary of the vortex. Finally, we compare our numerical results with the theoretical analysis of the short-time evolution of a buoyant vortex. Funded by the Spanish Ministry of Economy and Competitiveness through grant DPI2011-28356-C03-02 and by the London Mathematical Society.

  5. Drag of buoyant vortex rings.

    PubMed

    Vasel-Be-Hagh, Ahmadreza; Carriveau, Rupp; Ting, David S-K; Turner, John Stewart

    2015-10-01

    Extending from the model proposed by Vasel-Be-Hagh et al. [J. Fluid Mech. 769, 522 (2015)], a perturbation analysis is performed to modify Turner's radius by taking into account the viscous effect. The modified radius includes two terms; the zeroth-order solution representing the effect of buoyancy, and the first-order perturbation correction describing the influence of viscosity. The zeroth-order solution is explicit Turner's radius; the first-order perturbation modification, however, includes the drag coefficient, which is unknown and of interest. Fitting the photographically measured radius into the modified equation yields the time history of the drag coefficient of the corresponding buoyant vortex ring. To give further clarification, the proposed model is applied to calculate the drag coefficient of a buoyant vortex ring at a Bond number of approximately 85; a similar procedure can be applied at other Bond numbers. PMID:26565349

  6. Drag of buoyant vortex rings

    NASA Astrophysics Data System (ADS)

    Vasel-Be-Hagh, Ahmadreza; Carriveau, Rupp; Ting, David S.-K.; Turner, John Stewart

    2015-10-01

    Extending from the model proposed by Vasel-Be-Hagh et al. [J. Fluid Mech. 769, 522 (2015), 10.1017/jfm.2015.126], a perturbation analysis is performed to modify Turner's radius by taking into account the viscous effect. The modified radius includes two terms; the zeroth-order solution representing the effect of buoyancy, and the first-order perturbation correction describing the influence of viscosity. The zeroth-order solution is explicit Turner's radius; the first-order perturbation modification, however, includes the drag coefficient, which is unknown and of interest. Fitting the photographically measured radius into the modified equation yields the time history of the drag coefficient of the corresponding buoyant vortex ring. To give further clarification, the proposed model is applied to calculate the drag coefficient of a buoyant vortex ring at a Bond number of approximately 85; a similar procedure can be applied at other Bond numbers.

  7. Buoyant density constancy of Schizosaccharomyces pombe cells

    SciTech Connect

    Kubitschek, H.E.; Ward, R.A.

    1985-06-01

    Buoyant densities of cells from exponentially growing cultures of the fission yeast Schizosaccharomyces pombe 972h/sup -/ with division rates from 0.14 to 0.5 per h were determined by equilibrium centrifugation in Percoll gradients. Buoyant densities were independent of growth rate, with an average value (+/- standard error) of 1.0945 (+/- 0.00037) g/ml. When cells from these cultures were separated by size, mean cell volumes were independent of buoyant density, indicating that buoyant densities also were independent of cell age during the division cycle. These results support the suggestion that most or all kinds of cells that divide by equatorial fission may have similar, evolutionarily conserved mechanisms for regulation of buoyant density.

  8. Wind influence on a coastal buoyant outflow

    NASA Astrophysics Data System (ADS)

    Whitney, Michael M.; Garvine, Richard W.

    2005-03-01

    This paper investigates the interplay between river discharge and winds in forcing coastal buoyant outflows. During light winds a plume influenced by the Earth's rotation will flow down shelf (in the direction of Kelvin wave propagation) as a slender buoyancy-driven coastal current. Downwelling favorable winds augment this down-shelf flow, narrow the plume, and mix the water column. Upwelling favorable winds drive currents that counter the buoyancy-driven flow, spread plume waters offshore, and rapidly mix buoyant waters. Two criteria are developed to assess the wind influence on a buoyant outflow. The wind strength index (Ws) determines whether a plume's along-shelf flow is in a wind-driven or buoyancy-driven state. Ws is the ratio of the wind-driven and buoyancy-driven along-shelf velocities. Wind influence on across-shelf plume structure is rated with a timescale (ttilt) for the isopycnal tilting caused by wind-driven Ekman circulation. These criteria are used to characterize wind influence on the Delaware Coastal Current and can be applied to other coastal buoyant outflows. The Delaware buoyant outflow is simulated for springtime high-river discharge conditions. Simulation results and Ws values reveal that the coastal current is buoyancy-driven most of the time (∣Ws∣ < 1 on average). Wind events, however, overwhelm the buoyancy-driven flow (∣Ws∣ > 1) several times during the high-discharge period. Strong upwelling events reverse the buoyant outflow; they constitute an important mechanism for transporting fresh water up shelf. Across-shelf plume structure is more sensitive to wind influence than the along-shelf flow. Values of ttilt indicate that moderate or strong winds persisting throughout a day can modify plume width significantly. Plume widening during upwelling events is accompanied by mixing that can erase the buoyant outflow.

  9. Buoyant station mission comcepts for titan exploration

    NASA Astrophysics Data System (ADS)

    Friedlander, A. L.

    1985-10-01

    An advanced mission to this unique satellite of Saturn appropriate to the turn-of-the-century time period is described. The mission concept evolves about one or more buoyant stations (balloons and/or airship) operating at varying altitudes in Titan's atmosphere. An orbiter of Titan provides communications link support and accomplishes remote sensing science objectives. Use of buoyant stations are favored over a fixed site lander for two reasons: (1) adaptable to several possible surface physical states and topographies; and (2) capable of exploring both the atmosphere and surface with regional and possibly global mobility. Auxiliary payload concepts investigated include tethered packages and sounding rockets deployed from the buoyant station, and haze probes and surface penetrators deployed from the orbiter. The paper describes science objectives and payloads, propulsion system/mass delivery trades, balloon design requirements and deployment/motion characteristics, and communications link geometry and data characteristics.

  10. MERGING BUOYANT JETS IN A STRATIFIED CROSSFLOW

    EPA Science Inventory

    Some of the results of an extensive series of experiments to study the characteristics of merging, horizontally discharged buoyant jets in a linearly density stratified current are summarized. The experiments were conducted in a towing tank to simulate conditions typical of ocean...

  11. Effects of buoyant forces on chaotic electroconvection

    NASA Astrophysics Data System (ADS)

    Karatay, Elif; Wessling, Matthias; Mani, Ali; Stanford University, Department of Mechanical Engineering Collaboration; RWTH Aachen University, Department of Chemical Engineering Collaboration

    2015-11-01

    The transport of ionic species is enhanced by induced electroconvection that arise due to electrokinetic instabilities stemming from coupling of hydrodynamics with ion transport and electrostatic forces. Recent research have shown the contribution of chaotic multi-scale structures beyond a threshold value of applied electric potential. However the buoyant forces have been neglected in the existing studies of chaotic electrokinetic flows where the density gradients of salt depletion can become gravitationally stable or unstable depending on the geometric orientation of electrokinetic systems. In this study we thoroughly examine the interplay of gravitational convection and chaotic induced electroconvection in both gravitationally stable and unstable configurations via direct numerical simulations of a model system consisting of a salt solution confined in between two cation selective membranes. Our results reveal that buoyant forces are not negligible when the Rayleigh number of the system exceeds a critical value Racr ~ 1000 . When the density gradient of salt depletion is gravitationally stable, the growth of the electrokinetic flow structures are saturated by buoyant forces. Whereas gravitationally unstable density gradient leads to buoyant flow structures. Supported by Netherlands Organization for Scientific Research, Rubicon Grant.

  12. 46 CFR 131.870 - Life floats and buoyant apparatus.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Life floats and buoyant apparatus. 131.870 Section 131... OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.870 Life floats and buoyant apparatus. (a) The name of the vessel must be plainly marked or painted on each life float or buoyant...

  13. 46 CFR 131.870 - Life floats and buoyant apparatus.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Life floats and buoyant apparatus. 131.870 Section 131... OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.870 Life floats and buoyant apparatus. (a) The name of the vessel must be plainly marked or painted on each life float or buoyant...

  14. 46 CFR 131.870 - Life floats and buoyant apparatus.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Life floats and buoyant apparatus. 131.870 Section 131... OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.870 Life floats and buoyant apparatus. (a) The name of the vessel must be plainly marked or painted on each life float or buoyant...

  15. 46 CFR 108.697 - Buoyant work vests.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Buoyant work vests. 108.697 Section 108.697 Shipping... EQUIPMENT Miscellaneous Equipment § 108.697 Buoyant work vests. (a) Each buoyant work vest on a unit must be... work vests must be— (1) Used, stowed, and maintained in accordance with the procedures set out in...

  16. 46 CFR 108.697 - Buoyant work vests.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Buoyant work vests. 108.697 Section 108.697 Shipping... EQUIPMENT Miscellaneous Equipment § 108.697 Buoyant work vests. (a) Each buoyant work vest on a unit must be... work vests must be— (1) Used, stowed, and maintained in accordance with the procedures set out in...

  17. 46 CFR 108.697 - Buoyant work vests.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Buoyant work vests. 108.697 Section 108.697 Shipping... EQUIPMENT Miscellaneous Equipment § 108.697 Buoyant work vests. (a) Each buoyant work vest on a unit must be... work vests must be— (1) Used, stowed, and maintained in accordance with the procedures set out in...

  18. 46 CFR 131.870 - Life floats and buoyant apparatus.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.870 Life floats and buoyant apparatus. (a) The name of the vessel must be plainly marked or painted on each life float or buoyant apparatus... 46 Shipping 4 2010-10-01 2010-10-01 false Life floats and buoyant apparatus. 131.870 Section...

  19. 46 CFR 131.870 - Life floats and buoyant apparatus.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.870 Life floats and buoyant apparatus. (a) The name of the vessel must be plainly marked or painted on each life float or buoyant apparatus... 46 Shipping 4 2011-10-01 2011-10-01 false Life floats and buoyant apparatus. 131.870 Section...

  20. 46 CFR 108.697 - Buoyant work vests.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Buoyant work vests. 108.697 Section 108.697 Shipping... EQUIPMENT Miscellaneous Equipment § 108.697 Buoyant work vests. (a) Each buoyant work vest on a unit must be... work vests must be— (1) Used, stowed, and maintained in accordance with the procedures set out in...

  1. EXPERIMENTS ON BUOYANT PLUME DISPERSION IN A LABORATORY CONVENTION TANK

    EPA Science Inventory

    Buoyant plume dispersion in the convective boundary layer (CBL) is investigated experimentally in a laboratory convection tank. The focus is on highly-buoyant plumes that loft near the CBL capping inversion and resist downward mixing. Highly- buoyant plumes are those with dimen...

  2. BUOYANT ADVECTION OF GASES IN UNSATURATED SOIL

    PubMed Central

    Seely, Gregory E.; Falta, Ronald W.; Hunt, James R.

    2010-01-01

    In unsaturated soil, methane and volatile organic compounds can significantly alter the density of soil gas and induce buoyant gas flow. A series of laboratory experiments was conducted in a two-dimensional, homogeneous sand pack with gas permeabilities ranging from 110 to 3,000 darcy. Pure methane gas was injected horizontally into the sand and steady-state methane profiles were measured. Experimental results are in close agreement with a numerical model that represents the advective and diffusive components of methane transport. Comparison of simulations with and without gravitational acceleration permits identification of conditions where buoyancy dominates methane transport. Significant buoyant flow requires a Rayleigh number greater than 10 and an injected gas velocity sufficient to overcome dilution by molecular diffusion near the source. These criteria allow the extension of laboratory results to idealized field conditions for methane as well as denser-than-air vapors produced by volatilizing nonaqueous phase liquids trapped in unsaturated soil. PMID:20396624

  3. Buoyant densities of phototrophic sulfur bacteria and cyanobacteria

    NASA Technical Reports Server (NTRS)

    Guerrero, R.

    1985-01-01

    The buoyant densities of bacterial cells are greatly influenced by the accumulation of intracellular reserve material. The buoyant density of phototrophic bacteria that are planktonic is of particular interest, since these organisms must remain in the photic zone of the water column for optimal growth. Separation of cells by their buoyant density may also be of use in separating and identifying organisms from a natural population. The bacteria used were obtained from pure cultures, enrichments, or samples taken directly from the environment.

  4. Turbulence attenuation by large neutrally buoyant particles

    NASA Astrophysics Data System (ADS)

    Cisse, M.; Saw, E.-W.; Gibert, M.; Bodenschatz, E.; Bec, J.

    2015-06-01

    Turbulence modulation by inertial-range-size, neutrally buoyant particles is investigated experimentally in a von Kármán flow. Increasing the particle volume fraction Φv, maintaining constant impellers Reynolds number attenuates the fluid turbulence. The inertial-range energy transfer rate decreases as ∝ Φv 2 / 3 , suggesting that only particles located on a surface affect the flow. Small-scale turbulent properties, such as structure functions or acceleration distribution, are unchanged. Finally, measurements hint at the existence of a transition between two different regimes occurring when the average distance between large particles is of the order of the thickness of their boundary layers.

  5. 46 CFR 160.010-6 - Capacity of buoyant apparatus.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Buoyant Apparatus for Merchant Vessels § 160.010... immersed or where facilities are provided for climbing on top of the apparatus. (2) Number of 300 mm (1 ft... 46 Shipping 6 2010-10-01 2010-10-01 false Capacity of buoyant apparatus. 160.010-6 Section...

  6. 46 CFR 160.010-6 - Capacity of buoyant apparatus.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Buoyant Apparatus for Merchant Vessels § 160.010... immersed or where facilities are provided for climbing on top of the apparatus. (2) Number of 300 mm (1 ft... 46 Shipping 6 2011-10-01 2011-10-01 false Capacity of buoyant apparatus. 160.010-6 Section...

  7. Buoyant currents arrested by convective dissolution

    NASA Astrophysics Data System (ADS)

    MacMinn, Christopher W.; Juanes, Ruben

    2013-05-01

    When carbon dioxide (CO2) dissolves into water, the density of water increases. This seemingly insubstantial phenomenon has profound implications for geologic carbon sequestration. Here we show, by means of laboratory experiments with analog fluids, that the up-slope migration of a buoyant current of CO2 is arrested by the convective dissolution that ensues from a fingering instability at the moving CO2-groundwater interface. We consider the effectiveness of convective dissolution as a large-scale trapping mechanism in sloping aquifers, and we show that a small amount of slope is beneficial compared to the horizontal case. We study the development and coarsening of the fingering instability along the migrating current and predict the maximum migration distance of the current with a simple sharp-interface model. We show that convective dissolution exerts a powerful control on CO2 plume dynamics and, as a result, on the potential of geologic carbon sequestration.

  8. A turbulence model for buoyant flows based on vorticity generation.

    SciTech Connect

    Domino, Stefan Paul; Nicolette, Vernon F.; O'Hern, Timothy John; Tieszen, Sheldon R.; Black, Amalia Rebecca

    2005-10-01

    A turbulence model for buoyant flows has been developed in the context of a k-{var_epsilon} turbulence modeling approach. A production term is added to the turbulent kinetic energy equation based on dimensional reasoning using an appropriate time scale for buoyancy-induced turbulence taken from the vorticity conservation equation. The resulting turbulence model is calibrated against far field helium-air spread rate data, and validated with near source, strongly buoyant helium plume data sets. This model is more numerically stable and gives better predictions over a much broader range of mesh densities than the standard k-{var_epsilon} model for these strongly buoyant flows.

  9. Buoyant Bubbles and the Disturbed Cool Core of Abell 133

    NASA Astrophysics Data System (ADS)

    Randall, Scott W.; Clarke, T.; Nulsen, P.; Owers, M.; Sarazin, C.; Forman, W.; Jones, C.; Murray, S.

    2010-03-01

    X-ray cavities, often filled with radio-emitting plasma, are routinely observed in the intracluster medium of clusters of galaxies. These cavities, or "bubbles", are evacuated by jets from central AGN and subsequently rise buoyantly, playing a vital role in the "AGN feedback" model now commonly evoked to explain the balance between heating and radiative cooling in cluster cores. As the bubbles rise, they can displace cool central gas, promoting mixing and the redistribution of metals. I will show a few examples of buoyant bubbles, then argue that the peculiar morphology of the Abell 133 is due to buoyant lifting of cool central gas by a radio-filled bubble.

  10. Arc Evolution in Response to the Subduction of Buoyant Features

    NASA Astrophysics Data System (ADS)

    Jenkins, Luke; Fourel, Loic; Goes, Saskia; Morra, Gabriele

    2015-04-01

    The subduction of buoyant features such as aseismic ridges or oceanic plateaux has been invoked to explain arc deformation, flat subduction and increase in seismic coupling. Other studies have challenged these ideas, attributing a larger role to the overriding plate. However, many open questions remain about the dynamics of the relative simple case of a single freely subducting plate. How big does a plateau need to be to change the arc shape? What is the control of plate's strength on the impact of buoyant features? How do the velocities adapt to the subduction of less dense material? In the present study, we propose a systematic approach in order to tackle these questions. We use a new 3-D coupled fluid-solid subduction model where the interaction between the slab and the isoviscous mantle is only calculated on the slab surface, significantly increasing computational efficiency. The oceanic plate rheology is visco-elasto-plastic and its top surface is free. We find that arc shape is significantly altered by the subduction of buoyant plateaux. Along the subduction plane through the plateau and depending on its size, the dip angle and the retreat velocity significantly decrease. Flat subduction is obtained in the case of large and strongly buoyant plateau/ridge. An interesting feature is that retreat velocity increases right after the plateau or ridge has finished subducting in order to catch up with the rest of the plate. The gradient in retreat velocity obtained along the trench may cause the slab to have a heterogeneous response to ridge push, eventually leading to slab advance where buoyant material is present. We apply our models to the Izu-Bonin-Marianas (IBM) trench and propose that subduction of the buoyant Caroline Island Ridge at the southern edge of the Mariana trench can explain both trench motion history and the current morphology of the IBM slab as imaged by seismic tomography.

  11. Mixing by turbulent buoyant jets in slender containers

    NASA Astrophysics Data System (ADS)

    Voropayev, S. I.; Nath, C.; Fernando, H. J. S.

    2012-10-01

    A turbulent buoyant jet injected vertically into a slender cylinder containing a stratified fluid is investigated experimentally. The working fluid is water, and salt is used to change its density to obtain either a positively or negatively buoyant jet. The interest is the vertical density distribution in container and its dependence on time and other parameters. For each case (lighter or heavier jet) the experimental data could be collapsed into a ‘universal’ time dependent behavior, when properly non-dimensionalized. A theoretical model is advanced to explain the results. Possible applications include refilling of crude oil into U.S. strategic petroleum reserves caverns.

  12. Buoyant Magnetic Loops Generated by Global Convective Dynamo Action

    NASA Astrophysics Data System (ADS)

    Nelson, Nicholas J.; Brown, Benjamin P.; Sacha Brun, A.; Miesch, Mark S.; Toomre, Juri

    2014-02-01

    Our global 3D simulations of convection and dynamo action in a Sun-like star reveal that persistent wreaths of strong magnetism can be built within the bulk of the convention zone. Here we examine the characteristics of buoyant magnetic structures that are self-consistently created by dynamo action and turbulent convective motions in a simulation with solar stratification but rotating at three times the current solar rate. These buoyant loops originate within sections of the magnetic wreaths in which turbulent flows amplify the fields to much higher values than is possible through laminar processes. These amplified portions can rise through the convective layer by a combination of magnetic buoyancy and advection by convective giant cells, forming buoyant loops. We measure statistical trends in the polarity, twist, and tilt of these loops. Loops are shown to preferentially arise in longitudinal patches somewhat reminiscent of active longitudes in the Sun, although broader in extent. We show that the strength of the axisymmetric toroidal field is not a good predictor of the production rate for buoyant loops or the amount of magnetic flux in the loops that are produced.

  13. APPLICATION OF BUOYANT MASS TRANSFER MEDIA TO HAZARDOUS MATERIAL SPILLS

    EPA Science Inventory

    A prototype system was designed and developed to slurry buoyant activated carbon into a static body of water. The process was developed to remove spilled soluable hazardous compounds from a watercourse. In a simulated spill, up to 98% removal of Diazinon, an organophosphorus pest...

  14. Buoyant Nanoparticles: Implications for Nano-Biointeractions in Cellular Studies.

    PubMed

    Watson, C Y; DeLoid, G M; Pal, A; Demokritou, P

    2016-06-01

    In the safety and efficacy assessment of novel nanomaterials, the role of nanoparticle (NP) kinetics in in vitro studies is often ignored although it has significant implications in dosimetry, hazard ranking, and nanomedicine efficacy. It is demonstrated here that certain nanoparticles are buoyant due to low effective densities of their formed agglomerates in culture media, which alters particle transport and deposition, dose-response relationships, and underestimates toxicity and bioactivity. To investigate this phenomenon, this study determines the size distribution, effective density, and assesses fate and transport for a test buoyant NP (polypropylene). To enable accurate dose-response assessment, an inverted 96-well cell culture platform is developed in which adherent cells are incubated above the buoyant particle suspension. The effect of buoyancy is assessed by comparing dose-toxicity responses in human macrophages after 24 h incubation in conventional and inverted culture systems. In the conventional culture system, no adverse effects are observed at any NP concentration tested (up to 250 μg mL(-1) ), whereas dose-dependent decreases in viability and increases in reactive oxygen species are observed in the inverted system. This work sheds light on an unknown issue that plays a significant role in vitro hazard screening and proposes a standardized methodology for buoyant NP assessments. PMID:27135209

  15. Hands-On Experiences with Buoyant-Less Water

    ERIC Educational Resources Information Center

    Slisko, Josip; Planinsic, Gorazd

    2010-01-01

    The phenomenon of weightlessness is known to students thanks to videos of amazing things astronauts do in spaceships orbiting the Earth. In this article we propose two hands-on activities which give students opportunities to infer by themselves the absence of buoyant force in a gravity accelerated system. The system is a free-falling or vertically…

  16. 46 CFR 117.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 4 2012-10-01 2012-10-01 false Stowage of life floats and buoyant apparatus. 117.137... EQUIPMENT AND ARRANGEMENTS Survival Craft Arrangements and Equipment § 117.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 117.130, each life float and buoyant apparatus must...

  17. 46 CFR 117.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 4 2013-10-01 2013-10-01 false Stowage of life floats and buoyant apparatus. 117.137... EQUIPMENT AND ARRANGEMENTS Survival Craft Arrangements and Equipment § 117.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 117.130, each life float and buoyant apparatus must...

  18. 46 CFR 117.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 4 2014-10-01 2014-10-01 false Stowage of life floats and buoyant apparatus. 117.137... EQUIPMENT AND ARRANGEMENTS Survival Craft Arrangements and Equipment § 117.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 117.130, each life float and buoyant apparatus must...

  19. 46 CFR 117.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Stowage of life floats and buoyant apparatus. 117.137... EQUIPMENT AND ARRANGEMENTS Survival Craft Arrangements and Equipment § 117.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 117.130, each life float and buoyant apparatus must...

  20. 46 CFR 117.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Stowage of life floats and buoyant apparatus. 117.137... EQUIPMENT AND ARRANGEMENTS Survival Craft Arrangements and Equipment § 117.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 117.130, each life float and buoyant apparatus must...

  1. 46 CFR 160.010-5 - Buoyant apparatus with plastic foam buoyancy.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 6 2012-10-01 2012-10-01 false Buoyant apparatus with plastic foam buoyancy. 160.010-5 Section 160.010-5 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Buoyant Apparatus for Merchant Vessels § 160.010-5 Buoyant apparatus...

  2. 46 CFR 160.010-5 - Buoyant apparatus with plastic foam buoyancy.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 6 2013-10-01 2013-10-01 false Buoyant apparatus with plastic foam buoyancy. 160.010-5... Vessels § 160.010-5 Buoyant apparatus with plastic foam buoyancy. (a) Buoyant apparatus with plastic foam buoyancy must have a plastic foam body with an external protective covering. The body may be reinforced...

  3. 46 CFR 160.010-5 - Buoyant apparatus with plastic foam buoyancy.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 6 2011-10-01 2011-10-01 false Buoyant apparatus with plastic foam buoyancy. 160.010-5... Vessels § 160.010-5 Buoyant apparatus with plastic foam buoyancy. (a) Buoyant apparatus with plastic foam buoyancy must have a plastic foam body with an external protective covering. The body may be reinforced...

  4. 46 CFR 160.010-5 - Buoyant apparatus with plastic foam buoyancy.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 6 2014-10-01 2014-10-01 false Buoyant apparatus with plastic foam buoyancy. 160.010-5... Vessels § 160.010-5 Buoyant apparatus with plastic foam buoyancy. (a) Buoyant apparatus with plastic foam buoyancy must have a plastic foam body with an external protective covering. The body may be reinforced...

  5. 46 CFR 160.010-5 - Buoyant apparatus with plastic foam buoyancy.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 6 2010-10-01 2010-10-01 false Buoyant apparatus with plastic foam buoyancy. 160.010-5... Vessels § 160.010-5 Buoyant apparatus with plastic foam buoyancy. (a) Buoyant apparatus with plastic foam buoyancy must have a plastic foam body with an external protective covering. The body may be reinforced...

  6. 46 CFR 131.580 - Servicing of inflatable liferafts, inflatable lifejackets, inflatable buoyant apparatus, and...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... lifejackets, inflatable buoyant apparatus, and inflated rescue boats. 131.580 Section 131.580 Shipping COAST... Inspections § 131.580 Servicing of inflatable liferafts, inflatable lifejackets, inflatable buoyant apparatus, and inflated rescue boats. (a) An inflatable liferaft or inflatable buoyant apparatus must be...

  7. 46 CFR 131.580 - Servicing of inflatable liferafts, inflatable lifejackets, inflatable buoyant apparatus, and...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... lifejackets, inflatable buoyant apparatus, and inflated rescue boats. 131.580 Section 131.580 Shipping COAST... Inspections § 131.580 Servicing of inflatable liferafts, inflatable lifejackets, inflatable buoyant apparatus, and inflated rescue boats. (a) An inflatable liferaft or inflatable buoyant apparatus must be...

  8. Horizontal penetration of inclined thermal buoyant water jets

    SciTech Connect

    Pantokratoras, A.

    1998-05-01

    Submerged buoyant jets occur in the discharge from thermal power plants and in the operation of pumped storage hydroelectric plants. Accurate prediction of the jet trajectory and temperature dilution are necessary if discharge structures are to be designed to meet the appropriate standards. A modified version of the integral Fan-Brooks model has been used to calculate the horizontal penetration of inclined thermal buoyant water jets. The classical densimetric Froude number F{sub 0} is substituted by a Froude number F{sub a} based on the thermal expansion coefficient of water. Using the above model, a new equation is derived which can predict the horizontal penetration of the thermal jet at a given Froude number F{sub a} and discharge angle.

  9. Quantitative computational infrared imaging of buoyant diffusion flames

    NASA Astrophysics Data System (ADS)

    Newale, Ashish S.

    Studies of infrared radiation from turbulent buoyant diffusion flames impinging on structural elements have applications to the development of fire models. A numerical and experimental study of radiation from buoyant diffusion flames with and without impingement on a flat plate is reported. Quantitative images of the radiation intensity from the flames are acquired using a high speed infrared camera. Large eddy simulations are performed using fire dynamics simulator (FDS version 6). The species concentrations and temperature from the simulations are used in conjunction with a narrow-band radiation model (RADCAL) to solve the radiative transfer equation. The computed infrared radiation intensities rendered in the form of images and compared with the measurements. The measured and computed radiation intensities reveal necking and bulging with a characteristic frequency of 7.1 Hz which is in agreement with previous empirical correlations. The results demonstrate the effects of stagnation point boundary layer on the upstream buoyant shear layer. The coupling between these two shear layers presents a model problem for sub-grid scale modeling necessary for future large eddy simulations.

  10. Turbulence Statistics of a Buoyant Jet in a Stratified Environment

    NASA Astrophysics Data System (ADS)

    McCleney, Amy Brooke

    Using non-intrusive optical diagnostics, turbulence statistics for a round, incompressible, buoyant, and vertical jet discharging freely into a stably linear stratified environment is studied and compared to a reference case of a neutrally buoyant jet in a uniform environment. This is part of a validation campaign for computational fluid dynamics (CFD). Buoyancy forces are known to significantly affect the jet evolution in a stratified environment. Despite their ubiquity in numerous natural and man-made flows, available data in these jets are limited, which constrain our understanding of the underlying physical processes. In particular, there is a dearth of velocity field data, which makes it challenging to validate numerical codes, currently used for modeling these important flows. Herein, jet near- and far-field behaviors are obtained with a combination of planar laser induced fluorescence (PLIF) and multi-scale time-resolved particle image velocimetry (TR-PIV) for Reynolds number up to 20,000. Deploying non-intrusive optical diagnostics in a variable density environment is challenging in liquids. The refractive index is strongly affected by the density, which introduces optical aberrations and occlusions that prevent the resolution of the flow. One solution consists of using index matched fluids with different densities. Here a pair of water solutions - isopropanol and NaCl - are identified that satisfy these requirements. In fact, they provide a density difference up to 5%, which is the largest reported for such fluid pairs. Additionally, by design, the kinematic viscosities of the solutions are identical. This greatly simplifies the analysis and subsequent simulations of the data. The spectral and temperature dependence of the solutions are fully characterized. In the near-field, shear layer roll-up is analyzed and characterized as a function of initial velocity profile. In the far-field, turbulence statistics are reported for two different scales, one

  11. Density Driven Removal of Sediment from a Buoyant Muddy Plume

    NASA Astrophysics Data System (ADS)

    Rouhnia, M.; Strom, K.

    2014-12-01

    Experiments were conducted to study the effect of settling driven instabilities on sediment removal from hypopycnal plumes. Traditional approaches scale removal rates with particle settling velocity however, it has been suggested that the removal from buoyant suspensions happens at higher rates. The enhancement of removal is likely due to gravitational instabilities, such as fingering, at two-fluid interface. Previous studies have all sought to suppress flocculation, and no simple model exists to predict the removal rates under the effect of such instabilities. This study examines whether or not flocculation hampers instability formation and presents a simple removal rate model accounting for gravitational instabilities. A buoyant suspension of flocculated Kaolinite overlying a base of clear saltwater was investigated in a laboratory tank. Concentration was continuously measured in both layers with a pair of OBS sensors, and interface was monitored with digital cameras. Snapshots from the video were used to measure finger velocity. Samples of flocculated particles at the interface were extracted to retrieve floc size data using a floc camera. Flocculation did not stop creation of settling-driven fingers. A simple cylinder-based force balance model was capable of predicting finger velocity. Analogy of fingering process of fine grained suspensions to thermal plume formation and the concept of Grashof number enabled us to model finger spacing as a function of initial concentration. Finally, from geometry, the effective cross-sectional area was correlated to finger spacing. Reformulating the outward flux expression was done by substitution of finger velocity, rather than particle settling velocity, and finger area instead of total area. A box model along with the proposed outward flux was used to predict the SSC in buoyant layer. The model quantifies removal flux based on the initial SSC and is in good agreement with the experimental data.

  12. Magnetic Cycles and Buoyant Loops in Convective Dynamos

    NASA Astrophysics Data System (ADS)

    Nelson, Nicholas J.

    2013-01-01

    Solar-type stars display a rich spectrum of magnetic activity. Seeking to explore convective dynamo action in solar-like stars with the anelastic spherical harmonic (ASH) code, we have carried out a series of global 3-D MHD simulations. Here we report on the dynamo mechanisms realized in a series of numerical models of a sun-like star which explore the effects of decreasing diffusion. While these models nominally rotate at three times the current solar rate (3Ω), the results may be more widely applicable as both these simulations and the solar convection zone achieve similar levels of rotationally constrained convection. Previous simulations at 3Ω have shown that convective dynamos can build persistent wreath-like structures of strong toroidal magnetic field in the convection zone (Brown et al. 2010). Here we find that magnetic reversals and cycles can be realized at 3Ω by decreasing the explicit diffusion and thereby making the resolved flows more turbulent. In these more turbulent models, diffusive processes no longer play a primary role in the key dynamical balances which maintain differential rotation and generate the global-scale wreaths. With reduced resistive diffusion of magnetic fields, the axisymmetric poloidal fields can no longer achieve a steady state and this triggers reversals in global magnetic polarity. Additionally, the enhanced levels of turbulence lead to greater intermittency in the toroidal magnetic wreaths, which can create buoyant magnetic loops that rise from the deep interior to the upper regions of our simulated domain. Turbulence-enabled magnetic buoyancy in our most turbulent simulation yields large numbers of buoyant loops, enabling us to examine the distribution of the characteristics of buoyant magnetic loops, such as twist, tilt angle, and relation to axisymmetric fields. These models provide a pathway towards linking convective dynamo models and the emergence of magnetic flux in the Sun and sun-like stars.

  13. Self-concentrating buoyant glass microbubbles for high sensitivity immunoassays.

    PubMed

    Juang, Duane S; Hsu, Chia-Hsien

    2016-02-01

    Here, we report the novel application of a material with self-concentrating properties for enhancing the sensitivity of immunoassays. Termed as glass microbubbles, they are antibody functionalized buoyant hollow glass microspheres that simultaneously float and concentrate into a dense monolayer when dispensed in a liquid droplet. This self-concentrating charactaristic of the microbubbles allow for autonomous signal localization, which translates to a higher sensitivity compared to other microparticle-based immunoassays. We then demonstrated a "microbubble array" platform consisting of the glass microbubbles floating in a microfluidic liquid hemisphere array for performing multiplex immunoassays. PMID:26620967

  14. Buoyant triacylglycerol-filled green algae and methods therefor

    DOEpatents

    Goodenough, Ursula; Goodson, Carrie

    2015-04-14

    Cultures of Chlamydomonas are disclosed comprising greater than 340 mg/l triacylglycerols (TAG). The cultures can include buoyant Chlamydomonas. Methods of forming the cultures are also disclosed. In some embodiments, these methods comprise providing Chlamydomonas growing in log phase in a first culture medium comprising a nitrogen source and acetate, replacing the first culture medium with a second medium comprising acetate but no nitrogen source, and subsequently supplementing the second medium with additional acetate. In some embodiments, a culture can comprise at least 1,300 mg/l triacyglycerols. In some embodiments, cultures can be used to produce a biofuel such as biodiesel.

  15. The effects of Venus' thermal structure on buoyant magma ascent

    NASA Technical Reports Server (NTRS)

    Sakimoto, S. E. H.; Zuber, M. T.

    1992-01-01

    The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth.

  16. Wet and dry bacterial spore densities determined by buoyant sedimentation.

    PubMed Central

    Tisa, L S; Koshikawa, T; Gerhardt, P

    1982-01-01

    The wet densities of various types of dormant bacterial spores and reference particles were determined by centrifugal buoyant sedimentation in density gradient solutions of three commercial media of high chemical density. With Metrizamide or Renografin, the wet density values for the spores and permeable Sephadex beads were higher than those obtained by a reference direct mass method, and some spore populations were separated into several density bands. With Percoll, all of the wet density values were about the same as those obtained by the direct mass method, and only single density bands resulted. The differences were due to the partial permeation of Metrizamide and Renografin, but not Percoll, into the spores and the permeable Sephadex beads. Consequently, the wet density of the entire spore was accurately represented only by the values obtained with the Percoll gradient and the direct mass method. The dry densities of the spores and particles were determined by gravity buoyant sedimentation in a gradient of two organic solvents, one of high and the other of low chemical density. All of the dry density values obtained by this method were about the same as those obtained by the direct mass method. PMID:6285824

  17. A Model for Temperature Fluctuations in a Buoyant Plume

    NASA Astrophysics Data System (ADS)

    Bisignano, A.; Devenish, B. J.

    2015-11-01

    We present a hybrid Lagrangian stochastic model for buoyant plume rise from an isolated source that includes the effects of temperature fluctuations. The model is based on that of Webster and Thomson (Atmos Environ 36:5031-5042, 2002) in that it is a coupling of a classical plume model in a crossflow with stochastic differential equations for the vertical velocity and temperature (which are themselves coupled). The novelty lies in the addition of the latter stochastic differential equation. Parametrizations of the plume turbulence are presented that are used as inputs to the model. The root-mean-square temperature is assumed to be proportional to the difference between the centreline temperature of the plume and the ambient temperature. The constant of proportionality is tuned by comparison with equivalent statistics from large-eddy simulations (LES) of buoyant plumes in a uniform crossflow and linear stratification. We compare plume trajectories for a wide range of crossflow velocities and find that the model generally compares well with the equivalent LES results particularly when added mass is included in the model. The exception occurs when the crossflow velocity component becomes very small. Comparison of the scalar concentration, both in terms of the height of the maximum concentration and its vertical spread, shows similar behaviour. The model is extended to allow for realistic profiles of ambient wind and temperature and the results are compared with LES of the plume that emanated from the explosion and fire at the Buncefield oil depot in 2005.

  18. Phytoplankton productivity in a turbid buoyant coastal plume

    NASA Astrophysics Data System (ADS)

    Schofield, Oscar; Moline, Mark; Cahill, Brownyn; Frazer, Thomas; Kahl, Alex; Oliver, Matthew; Reinfelder, John; Glenn, Scott; Chant, Robert

    2013-07-01

    The complex dynamics associated with coastal buoyant plumes make it difficult to document the interactions between light availability, phytoplankton carbon fixation, and biomass accumulation. Using real-time data, provided by satellites and high frequency radar, we adaptively sampled a low salinity parcel of water that was exported from the Hudson river estuary in April 2005. The water was characterized by high nutrients and high chlorophyll concentrations. The majority of the low salinity water was re-circulated within a nearshore surface feature for 5 days during which nitrate concentrations dropped 7-fold, the maximum quantum yield for photosynthesis dropped 10-fold, and primary productivity rates decreased 5-fold. Associated with the decline in nitrate was an increase in phytoplankton biomass. The phytoplankton combined with the Colored Dissolved Organic Matter (CDOM) and non-algal particles attenuated the light so the 1% light level ranged between 3 and 10m depending on the age of the plume water. As the plume was 10-15m thick, the majority of the phytoplankton were light-limited. Vertical mixing within the plume was high as indicated by the dispersion of injected of rhodamine dye. The mixing within the buoyant plume was more rapid than phytoplankton photoacclimation processes. Mixing rates within the plume was the critical factor determining overall productivity rates within the turbid plume.

  19. Turbulence Statistics of a Buoyant Jet in a Stratified Environment

    NASA Astrophysics Data System (ADS)

    McCleney, Amy Brooke

    Using non-intrusive optical diagnostics, turbulence statistics for a round, incompressible, buoyant, and vertical jet discharging freely into a stably linear stratified environment is studied and compared to a reference case of a neutrally buoyant jet in a uniform environment. This is part of a validation campaign for computational fluid dynamics (CFD). Buoyancy forces are known to significantly affect the jet evolution in a stratified environment. Despite their ubiquity in numerous natural and man-made flows, available data in these jets are limited, which constrain our understanding of the underlying physical processes. In particular, there is a dearth of velocity field data, which makes it challenging to validate numerical codes, currently used for modeling these important flows. Herein, jet near- and far-field behaviors are obtained with a combination of planar laser induced fluorescence (PLIF) and multi-scale time-resolved particle image velocimetry (TR-PIV) for Reynolds number up to 20,000. Deploying non-intrusive optical diagnostics in a variable density environment is challenging in liquids. The refractive index is strongly affected by the density, which introduces optical aberrations and occlusions that prevent the resolution of the flow. One solution consists of using index matched fluids with different densities. Here a pair of water solutions - isopropanol and NaCl - are identified that satisfy these requirements. In fact, they provide a density difference up to 5%, which is the largest reported for such fluid pairs. Additionally, by design, the kinematic viscosities of the solutions are identical. This greatly simplifies the analysis and subsequent simulations of the data. The spectral and temperature dependence of the solutions are fully characterized. In the near-field, shear layer roll-up is analyzed and characterized as a function of initial velocity profile. In the far-field, turbulence statistics are reported for two different scales, one

  20. 46 CFR 180.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 7 2012-10-01 2012-10-01 false Stowage of life floats and buoyant apparatus. 180.137... § 180.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 180.130, each life... other standard specified by the Commandant; (2) Of proper strength for the size of the life float...

  1. 46 CFR 180.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Stowage of life floats and buoyant apparatus. 180.137... § 180.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 180.130, each life... other standard specified by the Commandant; (2) Of proper strength for the size of the life float...

  2. 46 CFR 180.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 7 2013-10-01 2013-10-01 false Stowage of life floats and buoyant apparatus. 180.137... § 180.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 180.130, each life... other standard specified by the Commandant; (2) Of proper strength for the size of the life float...

  3. 46 CFR 180.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 7 2014-10-01 2014-10-01 false Stowage of life floats and buoyant apparatus. 180.137... § 180.137 Stowage of life floats and buoyant apparatus. (a) In addition to meeting § 180.130, each life... other standard specified by the Commandant; (2) Of proper strength for the size of the life float...

  4. 46 CFR 131.865 - Inflatable liferafts and inflatable buoyant apparatus.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Inflatable liferafts and inflatable buoyant apparatus... SUPPLY VESSELS OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.865 Inflatable liferafts and inflatable buoyant apparatus. The number of the inflatable liferaft or inflatable...

  5. 46 CFR 131.865 - Inflatable liferafts and inflatable buoyant apparatus.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Inflatable liferafts and inflatable buoyant apparatus... SUPPLY VESSELS OPERATIONS Markings for Fire Equipment and Emergency Equipment § 131.865 Inflatable liferafts and inflatable buoyant apparatus. The number of the inflatable liferaft or inflatable...

  6. Capillary trapping of buoyant particles within regions of emergent vegetation

    NASA Astrophysics Data System (ADS)

    Peruzzo, Paolo; Defina, Andrea; Nepf, Heidi

    2012-07-01

    The seeds of many aquatic plants are buoyant and thus transported at the water surface, where they are subject to surface tension that may enhance their retention within emergent vegetation. Specifically, seeds may be trapped by surface tension (i.e., by the Cheerios effect) at the surface-piercing interface of the vegetation. In this work we develop a physical model that predicts this mechanism of seed trapping, advancing the model proposed by Defina and Peruzzo (2010) that describes the propagation of floating particles through emergent vegetation. The emergent vegetation is simulated as an array of cylinders, randomly arranged, with the mean gap between cylinders far greater than the particle size, which prevents the trapping of particles between pairs of cylinders, referred to as net trapping. Laboratory experiments are used to guide and validate the model. The model also has good agreement with experimental data available in the literature for real seeds and more complex plant morphology.

  7. Settling of almost neutrally buoyant particles in homogeneous isotropic turbulence

    NASA Astrophysics Data System (ADS)

    van Hinsberg, Michel; Clercx, Herman; Toschi, Federico

    2015-11-01

    Settling of particles in a turbulent flow occurs in various industrial and natural phenomena, examples are clouds and waste water treatment. It is well known that turbulence can enhance the settling velocity of particles. Many studies have been done, numerically and experimentally to investigate this behavior for the case of ``heavy'' particles, with particle to fluid density ratios above 100. Here we investigate the case of almost neutrally buoyant particles, i.e. density ratios between 1 and 100. In the case of light particles the Maxey-Riley equations cannot be simplified to only the Stokes drag and gravity force as pressure gradient, added mass and Basset history force are important as well. We investigate the influence of these forces on the settling velocity of particles and show that the extra forces can both increase or decrease the settling velocity, depending on the combination of the Stokes number and gravity applied.

  8. Flow behaviour of negatively buoyant jets in immiscible ambient fluid

    NASA Astrophysics Data System (ADS)

    Geyer, A.; Phillips, J. C.; Mier-Torrecilla, M.; Idelsohn, S. R.; Oñate, E.

    2012-01-01

    In this paper we investigate experimentally the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid. Experiments are carried out by injecting a jet of dyed fresh water through a nozzle in the base of a cylindrical tank containing rapeseed oil. The fountain inlet flow rate and nozzle diameter were varied to cover a wide range of Richardson Ri (8 × 10-4 < Ri < 1.98), Reynolds Re (467 < Re < 5,928) and Weber We (2.40 < We < 308.56) numbers. Based on the Re, Ri and We values for the experiments, we have determined a regime map to define how these values may control the occurrence of the observed flow types. Whereas Ri plays a stronger role when determining the maximum penetration height, the effect of the Reynolds number is stronger predicting the flow behaviour for a specific nozzle diameter and injection velocity.

  9. Sampling and analysis of particles from buoyant hydrothermal plumes

    NASA Astrophysics Data System (ADS)

    Mottl, Michael J.

    The objective of our studies has been to identify the chemical processes that occur in the buoyant part of hydrothermal plumes and to evaluate their role in determining the ultimate fate of the hydrothermal input to the oceans. Our first such effort is described by Mottl and McConachy [1990]. Because the buoyant plume is a small feature that contains very large physical and chemical gradients, we have sampled it from manned submersibles. We have used two different samplers, both manufactured by General Oceanics in Miami: the Go-Flo bottle and the Chopstick sampler. Four Go-Flo bottles of 1.7 L capacity can readily be mounted on most submersibles, vertically and in a forward position in sight of the pilot's viewport and video cameras, without interfering with other operations on a dive. On Alvin they have typically been mounted on the outside starboard edge of the basket. On Turtle they were mounted on the outside edge of the port manipulator. We chose Go-Flo rather than Niskin bottles because the latter are prone to spillage when the rods attached to the end caps are bumped against an object such as the seafloor, as often happens on a submersible dive. Go-Flo bottles are also more easily rigged for pressure filtration than are Niskins. The main disadvantage of Go-Flo bottles vs. Niskins for this application is the internal silicone rubber ring that holds the ball valves in place on each end of the Go-Flo. This ring tends to trap large particles that are then difficult to dislodge and collect. The rings are also difficult to clean between dives.

  10. Persistence of Strain in Buoyant and Nonbuoyant Turbulent Nonpremixed Flames

    NASA Astrophysics Data System (ADS)

    Boratav, O.; Elghobashi, S.; Zhong, R.

    1997-11-01

    The effects of chemical reaction and buoyancy on the persistence of strain are studied in three different flows: i) Nonbuoyant flame, ii) Buoyant flame with gravity perpendicular to the initial fuel-oxidant interface (horizontal flame) and iii) Same as (ii), but gravity is parallel to the initial interface (vertical flame). The magnitude of the rate of strain S_ij relative to vorticity ω is measured by the angle ψ = tan-1(2 S_ijS_ij/ω \\cdot ω). Three mixture fraction, F, regions of distinct ψ characteristics are identified: 1) F>F_st, 2) Fbuoyant flames, regions and (2) are vorticity-dominated due to the large baroclinic vorticity production, i.e. ψ arrow 0, resulting in shifting the pdf's of the ω-strain eigendirection more towards the β direction than the α. In region (3), the vorticity production is negligible for all three flows and at all times, thus resulting in the persistence of strain dominance over vorticity, i.e. ψ ≈ π/2, enforcing the alignment of ω with the α eigendirection. Consequently, the nabla F transport equation shows that nabla F will be located in the β-γ plane near F_st. Since |γ| > |β|, the largest straining of nabla F will be mostly along the direction of the most compressive strain direction γ near F_st as observed in all three cases. Our DNS results show that in reacting flows, the peak scalar dissipation ɛF will be near F_st regardless of the presence of buoyancy.

  11. Sheathless hydrodynamic positioning of buoyant drops and bubbles inside microchannels

    NASA Astrophysics Data System (ADS)

    Stan, Claudiu A.; Guglielmini, Laura; Ellerbee, Audrey K.; Caviezel, Daniel; Stone, Howard A.; Whitesides, George M.

    2011-09-01

    Particles, bubbles, and drops carried by a fluid in a confined environment such as a pipe can be subjected to hydrodynamic lift forces, i.e., forces that are perpendicular to the direction of the flow. We investigated the positioning effect of lift forces acting on buoyant drops and bubbles suspended in a carrier fluid and flowing in a horizontal microchannel. We report experiments on drops of water in fluorocarbon liquid, and on bubbles of nitrogen in hydrocarbon liquid and silicone oil, inside microchannels with widths on the order of 0.1-1 mm. Despite their buoyancy, drops and bubbles could travel without contacting with the walls of channels; the most important parameters for reaching this flow regime in our experiments were the viscosity and the velocity of the carrier fluid, and the sizes of drops and bubbles. The dependencies of the transverse position of drops and bubbles on these parameters were investigated. At steady state, the trajectories of drops and bubbles approached the center of the channel for drops and bubbles almost as large as the channel, carried by rapidly flowing viscous liquids; among our experiments, these flow conditions were characterized by larger capillary numbers and smaller Reynolds numbers. Analytical models of lift forces developed for the flow of drops much smaller than the width of the channel failed to predict their transverse position, while computational fluid dynamic simulations of the experiments agreed better with the experimental measurements. The degrees of success of these predictions indicate the importance of confinement on generating strong hydrodynamic lift forces. We conclude that, inside microfluidic channels, it is possible to support and position buoyant drops and bubbles simply by flowing a single-stream (i.e., “sheathless”) carrier liquid that has appropriate velocity and hydrodynamic properties.

  12. Shapes of Buoyant and Nonbuoyant Methane Laminar Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Sunderland, Peter B.; Yuan, Zeng-Guang; Urban, David L.

    1997-01-01

    Laminar gas jet diffusion flames represent a fundamental combustion configuration. Their study has contributed to numerous advances in combustion, including the development of analytical and computational combustion tools. Laminar jet flames are pertinent also to turbulent flames by use of the laminar flamelet concept. Investigations into the shapes of noncoflowing microgravity laminar jet diffusion flames have primarily been pursued in the NASA Lewis 2.2-second drop tower, by Cochran and coworkers and by Bahadori and coworkers. These studies were generally conducted at atmospheric pressure; they involved soot-containing flames and reported luminosity lengths and widths instead of the flame-sheet dimensions which are of Greater value to theory evaluation and development. The seminal model of laminar diffusion flames is that of Burke and Schumann, who solved the conservation of momentum equation for a jet flame in a coflowing ambient by assuming the velocity of fuel, oxidizer and products to be constant throughout. Roper and coworkers improved upon this model by allowing for axial variations of velocity and found flame shape to be independent of coflow velocity. Roper's suggestion that flame height should be independent of gravity level is not supported by past or present observations. Other models have been presented by Klajn and Oppenheim, Markstein and De Ris, Villermaux and Durox, and Li et al. The common result of all these models (except in the buoyant regime) is that flame height is proportional to fuel mass flowrate, with flame width proving much more difficult to predict. Most existing flame models have been compared with shapes of flames containing soot, which is known to obscure the weak blue emission of flame sheets. The present work involves measurements of laminar gas jet diffusion flame shapes. Flame images have been obtained for buoyant and nonbuoyant methane flames burning in quiescent air at various fuel flow-rates, burner diameters and ambient

  13. A new Lagrangian method for modelling the buoyant plume rise

    NASA Astrophysics Data System (ADS)

    Alessandrini, Stefano; Ferrero, Enrico; Anfossi, Domenico

    2013-10-01

    A new method for the buoyant plume rise computation is proposed. Following Alessandrini and Ferrero (Phys A 388:1375-1387, 2009) a scalar transported by the particles and representing the temperature difference between the plume and the environment air is introduced. As a consequence, no more particles than those inside the plume have to be released to simulate the entrainment of the background air temperature. A second scalar, the vertical plume velocity, is assigned to each particle. In this way the entrainment is properly simulated and the plume rise is calculated from the local property of the flow. The model has been tested against data from two laboratory experiments in neutral and stable stratified flows. The comparison shows a good agreement. Then, we tested our new model against literature analytical formulae in a simple uniform neutral atmosphere, considering either the case of a single plume or the one of two plumes from adjacent stacks combining during the rising stage. Finally, a comparison of the model against an atmospheric tracer experiment (Bull Run), characterized by vertically non-homogeneous fields (wind velocity, temperature, velocity standard deviations and time scales), was performed. All the tests confirmed the satisfactory performance of the model.

  14. Highly buoyant bent-over plumes in a boundary layer

    NASA Astrophysics Data System (ADS)

    Tohidi, Ali; Kaye, Nigel B.

    2016-04-01

    Highly buoyant plumes, such as wildfire plumes, in low to moderate wind speeds have initial trajectories that are steeper than many industrial waste plumes. They will rise further into the atmosphere before bending significantly. In such cases the plume's trajectory will be influenced by the vertical variation in horizontal velocity of the atmospheric boundary layer. This paper examined the behavior of a plume in an unstratified environment with a power-law ambient velocity profile. Examination of previously published experimental measurements of plume trajectory show that inclusion of the boundary layer velocity profile in the plume model often provides better predictions of the plume trajectory compared to algebraic expressions developed for uniform flow plumes. However, there are many cases in which uniform velocity profile algebraic expressions are as good as boundary layer models. It is shown that it is only important to model the role of the atmospheric boundary layer velocity profile in cases where either the momentum length (square root of source momentum flux divided by the reference wind speed) or buoyancy length (buoyancy flux divided by the reference wind speed cubed) is significantly greater than the plume release height within the boundary layer. This criteria is rarely met with industrial waste plumes, but it is important in modeling wildfire plumes.

  15. Experimental and computational investigation of underwater buoyant oil jets

    NASA Astrophysics Data System (ADS)

    Berard, Leandre; Raessi, Mehdi; Bauer, Michael; Friedman, Peter; Codyer, Stephen; University of Massachusetts Dartmouth Team

    2013-11-01

    We present experimental and numerical results on the breakup of underwater positively buoyant oil jets at a wide range of Reynolds, Weber and Richardson numbers and several viscosity ratios. Three main jet breakup regimes are observed: atomization, skirt-type and pinch-off. A threshold Weber number for the atomization regime is found to be around 100, varying slightly with the jet Eötvös number. The Ohnesorge-Reynolds correlation proposed by Masutani and Adams as the boundary for the atomization regime is shown to be applicable to our broader data set as well. Results suggest that the breakup of a positive buoyancy-driven jet occurs only when the jet is accelerated to a point where the local Richardson number becomes less than 0.4, in which case the local Weber number is above 10. The numerical results reveal the mechanisms leading to formation of small droplets around the perimeter of energetic jets and umbrella-shaped jet separations at less energetic cases. The time-averaged lateral expansion of the simulated jets, representing four different conditions, are presented as a function of the height along the jet.

  16. A piezoelectric, flexural-disk, neutrally buoyant, underwater accelerometer.

    PubMed

    Moffett, M B; Trivett, D H; Klippel, P J; Baird, P D

    1998-01-01

    A piezoelectric, flexural-disk accelerometer for underwater use is composed of two PZT-5A lead zirconate-titanate disks that are bonded to an aluminum substrate. The substrate is edge-supported inside an aluminum housing. The housing is enclosed in syntactic foam so that the sensor is neutrally buoyant. The overall height is 1.0 in. (26 mm), the overall diameter is 1.9 in. (49 mm), and the total mass is 0.054 kg. With 25 ft (7.6 m) of (230 pF/m) cable attached, the sensitivity is -42 dB re 1 V-s(2)/m (-22 dB re 1 V/g), the capacitance is 5.0 nF, and the resonance frequency is 11 kHz. When used in conjuction with a Micro Networks MN3210 preamplifier, the spectral noise-equivalent acceleration floor is approximately -171 dB re 1 m/s(2)- radicalHz (-151 dB re 1 g/ radicalHz) at 5 kHz. PMID:18244296

  17. Role of buoyant flame dynamics in wildfire spread

    PubMed Central

    Finney, Mark A.; Cohen, Jack D.; Forthofer, Jason M.; McAllister, Sara S.; Gollner, Michael J.; Gorham, Daniel J.; Saito, Kozo; Akafuah, Nelson K.; Adam, Brittany A.; English, Justin D.

    2015-01-01

    Large wildfires of increasing frequency and severity threaten local populations and natural resources and contribute carbon emissions into the earth-climate system. Although wildfires have been researched and modeled for decades, no verifiable physical theory of spread is available to form the basis for the precise predictions needed to manage fires more effectively and reduce their environmental, economic, ecological, and climate impacts. Here, we report new experiments conducted at multiple scales that appear to reveal how wildfire spread derives from the tight coupling between flame dynamics induced by buoyancy and fine-particle response to convection. Convective cooling of the fine-sized fuel particles in wildland vegetation is observed to efficiently offset heating by thermal radiation until convective heating by contact with flames and hot gasses occurs. The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Discovery that ignition in wildfires is critically dependent on nonsteady flame convection governed by buoyant and inertial interaction advances both theory and the physical basis for practical modeling. PMID:26183227

  18. Buoyant dispersal of CO2 during geological storage

    NASA Astrophysics Data System (ADS)

    Hesse, M. A.; Woods, A. W.

    2010-01-01

    Carbon capture and storage is currently the only technology that may allow significant reductions in CO2 emissions from large point sources. Seismic images of geological CO2 storage show the rise of CO2 is influenced by horizontal shales. The buoyant CO2 spreads beneath impermeable barriers until a gap allows its upward migration. The large number and small scale of these barriers makes the prediction of the CO2 migration path and hence the magnitude of CO2 trapping very challenging. We show that steady buoyancy dominated flows in complex geometries can be modeled as a cascade of flux partitioning events. This approach allows the analysis of two-dimensional plume dispersal from a horizontal injection well. We show that the plume spreads laterally with height y above the source according to (y/h)1/2 L, where L is the width of the shales and h is their vertical separation. The fluid volume below successive shale layers, and therefore the magnitude of trapped CO2, increase as (y/h)5/4 above the source, so that every additional layer of barriers traps more CO2 than the one below. Upscaling small scale flow barriers by reducing the vertical permeability, common in numerical simulations of CO2 storage, does not capture the dispersion and trapping of the CO2 plume by the flow barriers.

  19. Buoyant Magnetic Flux Ropes and Convection: Evolution Prior to Emergence

    NASA Astrophysics Data System (ADS)

    Dorch, S. B. F.

    2003-10-01

    We have performed detailed numerical 3-d simulations of the interaction of buoyantly ascending twisted magnetic flux ropes and solar-like stratified convection (with surface cells similar to solar supergranules in size). Results are presented for three different cases -- corresponding to different amounts of initial field line twist -- that represents fundamentally different types of instabilities: the magnetic Rayleigh-Taylor instability in which case the flux rope disrupts and network patches are formed at surface cell boundaries; the kink instability that has been proposed as a mechanism for forming tightly packed δ-type spots; a stable flux rope where neither of the former instabilities arise, and the behavior of which is similar to classical text book flux tubes, except from a flux-loss due to the advective action of the convective flows. The simulations thus support the idea that the magnetic flux observed at the surface in bipolar regions are smaller, ceteris paribus, than that of the dynamo generated flux ropes near the bottom of the convection zone. Please note that this material is also available as an online htmladdnormallink{web-talk}{http://www.astro.su.se/ dorch/talks/01_CS12/}

  20. Role of buoyant flame dynamics in wildfire spread.

    PubMed

    Finney, Mark A; Cohen, Jack D; Forthofer, Jason M; McAllister, Sara S; Gollner, Michael J; Gorham, Daniel J; Saito, Kozo; Akafuah, Nelson K; Adam, Brittany A; English, Justin D

    2015-08-11

    Large wildfires of increasing frequency and severity threaten local populations and natural resources and contribute carbon emissions into the earth-climate system. Although wildfires have been researched and modeled for decades, no verifiable physical theory of spread is available to form the basis for the precise predictions needed to manage fires more effectively and reduce their environmental, economic, ecological, and climate impacts. Here, we report new experiments conducted at multiple scales that appear to reveal how wildfire spread derives from the tight coupling between flame dynamics induced by buoyancy and fine-particle response to convection. Convective cooling of the fine-sized fuel particles in wildland vegetation is observed to efficiently offset heating by thermal radiation until convective heating by contact with flames and hot gasses occurs. The structure and intermittency of flames that ignite fuel particles were found to correlate with instabilities induced by the strong buoyancy of the flame zone itself. Discovery that ignition in wildfires is critically dependent on nonsteady flame convection governed by buoyant and inertial interaction advances both theory and the physical basis for practical modeling. PMID:26183227

  1. AN EXPERIMENTAL/ANALYTICAL INVESTIGATION OF DEEP SUBMERGED MULTIPLE BUOYANT JETS

    EPA Science Inventory

    The results of an experimental and analytical study of deep submerged multiple-port thermal discharges are presented. The experimental results include the measured downstream thermal dilution, width, and centerline trajectory of the buoyant thermal plume from multiple port discha...

  2. Independence of buoyant cell density and growth rate in Escherichia coli

    SciTech Connect

    Kubitchek, H.E.; Baldwin, W.W.; Schroeter, S.J.; Graetzer, R.

    1984-04-01

    The relationship between growth rate and buoyant density was determined for cells from exponential-phase cultures of Escherichia coli B/r NC32 by equilibrium centrifugation in Percoll gradients at growth rates ranging from 0.15 to 2.3 doublings per h. The mean buoyant density did not change significantly with growth rate in any of three sets of experiments in which different gradient conditions were used. In addition, when cultures were allowed to enter the stationary phase of growth, mean cell volumes and buoyant densities usually remained unchanged for extended periods. These and earlier results support the existence of a highly regulated, discrete state of buoyant density during steady-state growth of E. coli and other cells that divide by equatorial fission. 11 references, 3 figures.

  3. Vehicle concepts and technology requirements for buoyant heavy-lift systems

    NASA Technical Reports Server (NTRS)

    Ardema, M. D.

    1981-01-01

    Several buoyant-vehicle (airship) concepts proposed for short hauls of heavy payloads are described. Numerous studies identified operating cost and payload capacity advantages relative to existing or proposed heavy-lift helicopters for such vehicles. Applications involving payloads of from 15 tons up to 800 tons were identified. The buoyant quad-rotor concept is discussed in detail, including the history of its development, current estimates of performance and economics, currently perceived technology requirements, and recent research and technology development. It is concluded that the buoyant quad-rotor, and possibly other buoyant vehicle concepts, has the potential of satisfying the market for very heavy vertical lift but that additional research and technology development are necessary. Because of uncertainties in analytical prediction methods and small-scale experimental measurements, there is a strong need for large or full-scale experiments in ground test facilities and, ultimately, with a flight research vehicle.

  4. Physical and Numerical Modeling of Buoyant Groundwater Plumes

    NASA Astrophysics Data System (ADS)

    Brakefield, L. K.; Abarca, E.; Langevin, C. D.; Clement, T. P.

    2007-12-01

    In coastal states, the injection of treated wastewater into deep saline aquifers offers a disposal alternative to ocean outfalls and discharge directly into local waterways. The density of treated wastewater is similar to that of freshwater but is often much lower than the ambient density of deep aquifers. This significant density contrast can cause upward buoyant movement of the wastewater plume during and after injection. Since some wastewater treatment plants inject more than 100 MGD of this treated wastewater, it is of the utmost importance to be able to not only determine the fate and transport rates of the plume, but to be able to best determine locations for monitoring wells for early detection of possible problems. In this study, both physical and numerical modeling were undertaken to investigate and understand buoyant plume behavior and transport. Physical models using a 2D cross-sectional Plexiglas tank filled with glass beads were carried out under different ambient density scenarios. The experiments consisted of injection of a freshwater pulse-source bubble into a fully saline tank. The injection occurred in an initially static system with no ambient flow. In the scenarios, the freshwater plume migrated vertically upward until reaching the top of the tank. Fingers developed because of the heterogeneity of the density dependent flow field. The vertical velocities and transport patterns of these plumes were compared to one another to investigate variances due to different ambient water densities. Using the finite-difference numerical code SEAWAT to simulate variable density flow, the experiments were numerically modeled and compared with the physical model results. Due to the sensitivity of this problem to numerical resolution, results from three different grids were compared to determine a reasonable compromise between computer runtimes and numerical accuracy. Furthermore, a comparison of advection solvers was undertaken to identify the best solver to

  5. Mass transport by buoyant bubbles in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Pope, Edward C. D.; Babul, Arif; Pavlovski, Georgi; Bower, Richard G.; Dotter, Aaron

    2010-08-01

    We investigate the effect of three important processes by which active galactic nuclei (AGN)-blown bubbles transport material: drift, wake transport and entrainment. The first of these, drift, occurs because a buoyant bubble pushes aside the adjacent material, giving rise to a net upward displacement of the fluid behind the bubble. For a spherical bubble, the mass of upwardly displaced material is roughly equal to half the mass displaced by the bubble and should be ~ 107-9 Msolar depending on the local intracluster medium (ICM) and bubble parameters. We show that in classical cool-core clusters, the upward displacement by drift may be a key process in explaining the presence of filaments behind bubbles. A bubble also carries a parcel of material in a region at its rear, known as the wake. The mass of the wake is comparable to the drift mass and increases the average density of the bubble, trapping it closer to the cluster centre and reducing the amount of heating it can do during its ascent. Moreover, material dropping out of the wake will also contribute to the trailing filaments. Mass transport by the bubble wake can effectively prevent the buildup of cool material in the central galaxy, even if AGN heating does not balance ICM cooling. Finally, we consider entrainment, the process by which ambient material is incorporated into the bubble. Studies of observed bubbles show that they subtend an opening angle much larger than predicted by simple adiabatic expansion. We show that bubbles that entrain ambient material as they rise will expand faster than the adiabatic prediction; however, the entrainment rate required to explain the observed opening angle is large enough that the density contrast between the bubble and its surroundings would disappear rapidly. We therefore conclude that entrainment is unlikely to be a dominant mass transport process. Additionally, this also suggests that the bubble surface is much more stable against instabilities that promote

  6. Wave induced transport and mixing of buoyant particles

    NASA Astrophysics Data System (ADS)

    Drivdal, Magnus; Broström, Göran; Christensen, Kai H.

    2014-05-01

    The modeling of wave-current and wave-turbulence interactions have received much attention during recent years. Both the breaking of surface waves and the inclusion of the Stokes shear production have been shown to increase the upper ocean turbulence. Furthermore the Coriolis force acting on the Stokes drift redistributes the momentum in the upper ocean, leading to a deflection of the currents. An important application affected by these processes that still needs to be studied is the mixing and drift of particles. Using an ocean column model, modified to take surface wave effects into account, we investigate how the increased mixing by wave breaking and Stokes shear production as well as the stronger veering by the Coriolis-Stokes force effects the drift of suspended particles. Here the suspended particles are buoyant tracers that can represent oil droplets or plankton, for example fish eggs and larvae. The energy and momentum fluxes as well as the Stokes drift depend on the directional wave spectrum that can be obtained from a wave model or from observations. Comparing with classical Ekman theory some physical effects on the system are studied, and as a realistic test case we use the model to study the oil drift after an offshore oil spill that took place outside the western coast of Norway in 2007. During this accident the average net drift of oil was observed to be approximately 0.1% of the wind speed at an angle of about 90-120 degrees to the right, far slower and more deflected away from the wind direction than predicted by both numerical and empirical models. With wind and wave forcing from ECMWF reanalysis data, it is shown that the wave effects are important for the resultant drift in this case, and has the potential to improve drift forecasting.

  7. Surface buoyant plumes from melting icebergs in the Labrador Sea

    NASA Astrophysics Data System (ADS)

    Yankovsky, Alexander E.; Yashayaev, Igor

    2014-09-01

    Canada's Department of Fisheries and Oceans (DFO) conducts annual surveys in the Labrador Sea along the repeat hydrography line AR7W. The occupation of the AR7W line in May 2013 was followed by the experiment aimed at resolving the imprint of melting drifting icebergs on the upper layer thermohaline characteristics in the Labrador Sea. We present high-resolution observations around two icebergs conducted with the towed undulating platform Moving Vessel Profiler (MVP). The first iceberg drifted in relatively warm water of Atlantic origin (~2.5-3.1 °C) off Greenland, while the second iceberg was on the Labrador shelf in cold water below 0 °C. Both icebergs had a lengthscale of O(100 m). In both cases surface buoyant plumes fed by melt water and attached to the iceberg were observed. The plumes were evident in the anomalous thermohaline characteristics of the seawater. Their density anomalies were sufficiently strong to produce visible frontal structures, which imply a development of the intrinsic dynamics associated with a plume. The first plume formed over a time interval of ~10 h, while the second plume formed over several days and extended for more than 1 km (tenfold the iceberg's size). Strong vertical displacements of the pycnocline were observed near the second iceberg. They are interpreted as the internal wave wake. This interpretation is based on the temporal scale of these oscillations (local buoyancy frequency), as well as on the spatial orientation of these waves with respect to the iceberg drift relative to the pycnocline. The observed internal waves partially overlapped with the plume and affected its structure. The saline seawater splashing by swell contributed to the surface melting of the icebergs. Scaling analysis of the second plume suggests that it could be in the “rotational” dynamic regime with recirculating anticyclonic flow.

  8. Numerical simulation of buoyant turbulent flow. Final report

    SciTech Connect

    Humphrey, J.A.C.; Sherman, F.S.; To, W.M.

    1985-08-01

    Two models have been developed for predicting low Reynolds number turbulent flows in the free and mixed convection regimes. One, the KEM model, is based on the notion of eddy diffusivities for momentum and heat. The other, the ASM model, is based on algebraic relations derived for the anisotropic turbulent fluxes by suitable truncation of the parent transport equations. Both formulations apply to variable property flows with high overheat ratios. A comparison between measurements and predictions for the case of the vertical plate shows that both models yield fairly accurate results for the mean flow and heat transfer. As a result, only the simpler of the two models, the KEM, was used to predict the cavity flows. Predictions for the case of the vertical flat plate show excellent agreement with measurements of mean velocity, temperature and Nusselt number. Nearwall results predicted by both models reveal the existence of a 1/3 power-law dependence. Regions of negative buoyant and shear production of turbulence kinetic energy are clearly revealed by the calculations. Calculations of the cavity configuration were performed for the free and mixed flow conditions. Fairly good agreement is obtained between measurements and predictions of the velocity and temperature fields. Many of the complex characteristics of heated cavity flows, revealed experimentally, are resolved numerically. Although differing in absolute value, calculations of the cavity Nusselt number show trends which are in accord with the measurements. Thus, in the free convection regime it is shown that when the cavity is tilted forwards stable stratification of fluid dampens the turbulence fluctuations which works to reduce heat transfer.

  9. Supergranulation as the Sun's largest buoyantly driven mode of convection

    NASA Astrophysics Data System (ADS)

    Cossette, Jean-Francois; Rast, Mark

    2016-05-01

    Solar supergranulation has been characterized as horizontally divergent flow motions having a typical scale of 32 Mm using Doppler imaging, granule tracking and helioseismology. Unlike granules, the size of which is comparable to both the thickness of the radiative boundary layer and local scale height at the photosphere, supergranules do not appear to correspond to any particular length scale of the flow. Possible explanations ranging from convection theories involving Helium ionization to spatial correlation or self-organization of granular flows have been proposed as physical mechanisms to explain solar supergranulation. However, its existence remains largely a mystery. Remarkably, horizontal velocity power spectra obtained from Doppler imaging and correlation tracking of flow features at the solar surface reveal the presence of peaks corresponding to granular and supergranular scales, followed by a monotonic decrease in power at scales larger than supergranulation, which suggests that large-scale modes in the deep layers of the convection zone may be suppressed. Using 3D anelastic simulations of solar convection we investigate whether supergranulation may reflect the largest buoyantly driven mode of convection inside the Sun. Results show that the amount of kinetic energy contained in the largest flow scales relative to that associated with supergranular motions is a function of the depth of the transition from a convectively unstable to convectively stable mean stratification inside the simulation. This suggests that the observed monotonic decrease in power at scales larger than supergranulation may be explained by rapid cooling in the subphotospheric layers and an essentially isentropic solar interior, wherein convective driving is effectively suppressed.

  10. Surface Buoyant Plumes from Melting Icebergs in the Labrador Sea

    NASA Astrophysics Data System (ADS)

    Yankovsky, Alexander; Yashayaev, Igor

    2014-05-01

    Canada's Department of Fisheries and Oceans (DFO) conducts annual surveys in the Labrador Sea along the repeat hydrography line AR7W. Since 2012, these shipboard surveys have been supplemented by underway CTD and optical measurements in the upper 200 m layer conducted with the towed undulating platform Moving Vessel Profiler (MVP). The MVP hydrographic data reveal rich variability of the upper layer salinity field on different spatial scales. The occupation of the AR7W line in May 2013 was followed by the experiment aimed at resolving the imprint of melting drifting icebergs on the upper layer thermohaline characteristics in the Labrador Sea. Here we present observations around two icebergs: the first iceberg drifted in relatively warm water of Atlantic origin (~2.5-3.1°C) off Greenland, while the second iceberg was on the Labrador shelf in cold water below 0°C. Both icebergs had a lengthscale of O(100 m). In both cases surface buoyant plumes fed by melt water and attached to the iceberg were observed. The plumes were evident in the anomalous thermohaline characteristics of the seawater. Their density anomalies were sufficiently strong to produce visible frontal structures, which imply a development of the intrinsic dynamics associated with a plume. The first plume formed over a time interval of ~10 hr, while the second plume formed over several days and extended for more than 1 km (tenfold the iceberg's size). Strong vertical displacements of the pycnocline were observed near the second iceberg. They are interpreted as the internal wave wake. This interpretation is based on the temporal scale of these oscillations (local buoyancy frequency), as well as on the spatial orientation of these waves with respect to the iceberg drift relative to the pycnocline. The observed internal waves partially overlapped with the plume and affected its structure. The saline seawater splashing by swell contributed to the surface melting of the icebergs. Scaling analysis of the

  11. A chemical model of the buoyant and neutrally buoyant plume above the TAG vent field, 26 degrees N, Mid-Atlantic Ridge

    NASA Astrophysics Data System (ADS)

    Rudnicki, M. D.; Elderfield, H.

    1993-07-01

    The kinetics of iron particle formation in the neutrally buoyant plume above the TAG vent field (26 degrees N, Mid-Atlantic Ridge) have been calculated from submersible-collected CTD data within the initial 150 m of plume rise. Results show that particles form by a two-stage process: about half the iron in the high temperature vent fluid is removed as sulfides within a few seconds of venting and the remainder is removed by Fe 2+ oxidation. The pseudo-first-order rate constant for the second process has been calculated ( k1 = 0.329min -1, similar to literature values for seawater) and gives a halflife time for Fe 2+ in solution of 2.1 minutes. The kinetics of iron particle formation have been used in a conceptual model of the chemistry of the TAG plume. The average dilution at which iron oxyhydroxide particles form, E¯ Fe, is ˜ 570 from which element/Fe ratios of particles at the top of the buoyant plume have been predicted. Oxyanion/Fe ratios can be chiefly accounted for by coprecipitation for Cr (71%), V (67%), As (45%) and P (42%) but Mo (0.1%) and U (0.02%) show anomalously low coprecipitation. Th/Fe and REE/Fe ratios are greater than can be accounted for by coprecipitation, demonstrating that scavenging occurs in the buoyant plume for these elements. 98% of the Th uptake and 15-75% of the REE uptake is by scavenging. Scavenging rate constants are 3.1 * 10 -6 (nmol/kg) -1 s -1 for Th and 1.4-33* 10 -8 (nmol/kg) -1 s -1 for the REE. A scavenging model has been fitted to trace metal data previously reported for neutrally buoyant hydrothermal plume particulate samples collected above the TAG vent field. The model is based on the assumption that there is a characteristic t1/2 for the dilution of the neutrally buoyant plume and this value has been calculated, by comparing 228Th and 230Th with 234Th isotope data, as fourty-one days (λ p = 0.0170 day -1). Scavenging rate constants are 2* 10 -9 (nmol/kg) -1 s -1 for Th and 3.5-16*10 -11 (nmol/kg) -1 s -1 for the REE

  12. Oil-entrapped sterculia gum-alginate buoyant systems of aceclofenac: development and in vitro evaluation.

    PubMed

    Guru, Pravat Ranjan; Nayak, Amit Kumar; Sahu, Rajendra Kumar

    2013-04-01

    The current investigation deals with the development and optimization of oil-entrapped sterculia gum-alginate buoyant beads containing aceclofenac by ionotropic emulsion-gelation technique using 3(2) factorial design. The effect of polymer to drug ratio and sodium alginate to sterculia gum ratio on the drug entrapment efficiency (%), and cumulative drug release after 7 h (%) was optimized. The optimized oil-entrapped sterculia gum-alginate buoyant beads containing aceclofenac (F-O) showed drug entrapment efficiency of 90.92±2.34%, cumulative drug release of 41.65±3.97% after 7 h in simulated gastric fluid (pH 1.2), and well buoyancy over 8 h in simulated gastric fluid (pH 1.2) with 5.20 min buoyant lag-time. The in vitro drug release from these buoyant beads followed Korsmeyer-Peppas model (R(2)=0.9866-0.9995) with anomalous (non-Fickian) diffusion drug release mechanism. These new sterculia gum-alginate buoyant beads containing aceclofenac were also characterized using SEM, FTIR, and P-XRD analysis. PMID:23334180

  13. Spatial DNS of flow transition of a rectangular buoyant reacting free-jet*

    NASA Astrophysics Data System (ADS)

    Jiang, X.; Luo, K. H.

    2001-10-01

    This paper describes a spatial direct numerical simulation (DNS) of the flow transition of a buoyant diffusion flame established on a rectangular nozzle with an aspect ratio of 2:1. Combustion is represented by a one-step finite-rate Arrhenius chemistry. Without applying external perturbations, large vortical structures develop naturally in the flow field due to buoyancy effects. The vortex dynamics of the rectangular buoyant reacting jet has been analysed. The interaction between density gradients and gravity initiates the flow vorticity in the cross-streamwise directions. The streamwise vorticity is mainly generated by the vortex stretching. Downstream of the reacting jet, a more disorganized flow regime characterized by small scales has been observed, following the breakdown of the large vortical structures due to three-dimensional vortex interactions. Analysis of the energy spectra shows that the spatially developing reacting jet has a tendency of transition to turbulence under the effects of combustion-induced buoyancy. Buoyancy effects are found to be very important to the formation, development, interaction and breakdown of vortices. In contrast with the relaminarization effects of chemical exothermicity on non-buoyant jet diffusion flames via volumetric expansion and viscous damping, the tendency towards transition to turbulence in buoyant reacting jets is greatly enhanced by the overwhelming buoyancy effects. Calculations of the mean flow property show that the rectangular buoyant reacting jet has a higher entrainment rate than its non-reacting counterpart.

  14. Powering of cool filaments in cluster cores by buoyant bubbles - I. Qualitative model

    NASA Astrophysics Data System (ADS)

    Churazov, E.; Ruszkowski, M.; Schekochihin, A.

    2013-11-01

    Cool-core clusters (e.g. Perseus or M87) often possess a network of bright gaseous filaments, observed in radio, infrared, optical and X-ray bands. We propose that these filaments are powered by the reconnection of the magnetic field in the wakes of buoyant bubbles. Active galactic nucleus (AGN)-inflated bubbles of relativistic plasma rise buoyantly in the cluster atmosphere, stretching and amplifying the field in the wake to values of β = 8πPgas/B2 ˜ 1. The field lines in the wake have opposite directions and are forced together as the bubble motion stretches the filament. This setup bears strong similarity to the coronal loops on the Sun or to the Earth's magnetotail. The reconnection process naturally explains both the required level of local dissipation rate in filaments and the overall luminosity of filaments. The original source of power for the filaments is the potential energy of buoyant bubbles, inflated by the central AGN.

  15. A Lagrangian particle random walk model for simulating a deep-sea hydrothermal plume with both buoyant and non-buoyant features

    NASA Astrophysics Data System (ADS)

    Tian, Yu; Li, Wei; Zhang, Ai-qun

    2013-04-01

    This paper presents a computational model of simulating a deep-sea hydrothermal plume based on a Lagrangian particle random walk algorithm. This model achieves the efficient process to calculate a numerical plume developed in a fluid-advected environment with the characteristics such as significant filament intermittency and significant plume meander due to flow variation with both time and location. Especially, this model addresses both non-buoyant and buoyant features of a deep-sea hydrothermal plume in three dimensions, which significantly challenge a strategy for tracing the deep-sea hydrothermal plume and localizing its source. This paper also systematically discusses stochastic initial and boundary conditions that are critical to generate a proper numerical plume. The developed model is a powerful tool to evaluate and optimize strategies for the tracking of a deep-sea hydrothermal plume via an autonomous underwater vehicle (AUV).

  16. Preliminary study of ground handling characteristics of Buoyant Quad Rotor (BQR) vehicles

    NASA Technical Reports Server (NTRS)

    Browning, R. G. E.

    1980-01-01

    A preliminary investigation of mooring concepts appropriate for heavy lift buoyant quad rotor (BQR) vehicles was performed. A review of the evolution of ground handling systems and procedures for all airship types is presented to ensure that appropriate consideration is given to past experiences. Two buoyant quad rotor designs are identified and described. An analysis of wind loads on a moored airship and the effects of these loads on vehicle design is provided. Four mooring concepts are assessed with respect to the airship design, wind loads and mooring site considerations. Basing requirements and applicability of expeditionary mooring at various operational scenarios are addressed.

  17. Note: Buoyant-force assisted liquid membrane electrochemical etching for nano-tip preparation.

    PubMed

    Zeng, Yongbin; Wang, Yufeng; Wu, Xiujuan; Xu, Kun; Qu, Ningsong

    2014-12-01

    A liquid membrane electrochemical etching process for preparing nano-tips is proposed by the introduction of buoyant force to the lower tip, in which the lower portion of the anodic wire is immersed into a floating layer. A mathematical model of this method is derived. Both calculation and experimental results demonstrate that the introduction of buoyant force can significantly decrease the tip radius. The lubricating oil and deionized water floating layers were tested for the processing of nano-tips. Further, high-aspect-ratio nano-electrodes were prepared by applying a relative vertical movement to the anodic wire. PMID:25554341

  18. Structure and Soot Properties of Non-Buoyant Laminar Round-Jet Diffusion Flames

    NASA Technical Reports Server (NTRS)

    Mortazavi, Saeed; Sunderland, Peter B.; Jurng, Jongsoo; Faeth, Gerard M.

    1993-01-01

    The structure and soot properties of nonbuoyant laminar diffusion flames are being studied experimentally and theoretically in order to better understand the soot and thermal radiation emissions from luminous flames. The measurements involve weakly-buoyant flames at low pressure in normal gravity (ng) and nonbuoyant flames at normal pressures in microgravity (micro g). The objectives of the present investigation are to study the differences of soot properties between nonbuoyant and buoyant diffusion flames, and to evaluate predictions based on the laminar flamelet approach.

  19. A chemical model of the buoyant and neutrally buoyant plume above the TAG vent field, 26 degrees N, Mid-Atlantic Ridge

    SciTech Connect

    Rudnicki, M.D.; Elderfield, H. )

    1993-07-01

    The kinetics of iron particle formation in the neutrally buoyant plume above the TAG vent field have been calculated from submersible-collected CTD data within the initial 150 m of plume rise. Results show that particles form by a two-stage process: about half the iron in the high temperature vent fluid is removed as sulfides within a few seconds of venting, and the remainder is removed by Fe[sup 2+] oxidation. The pseudo-first-order rate constant for the second process has been calculated (k[sub 1] = 0.329 min[sup [minus]1], similar to literature values for seawater) and gives a half-life time for Fe[sup 2+] in solution of 2.1 minutes. The kinetics of iron particle formation have been used in a conceptual model of the chemistry of the TAG plume. The average dilution at which iron oxyhydroxide particles form, [bar E][sub Fe], is [approximately]570 from which element/Fe ratios of particles at the top of the buoyant plume have been predicted. Oxyanion/Fe ratios can be chiefly accounted for by coprecipitation for Cr (71%), V (67%), As (45%), and P (42%) but Mo (0.1%) and U (0.02%) show anomalously low coprecipitation. Th/Fe and REE/Fe ratios are greater than can be accounted for by coprecipitation, demonstrating that scavenging occurs in the buoyant plume for these elements. A scavenging model has been fitted to trace metal data previously reported for neutrally buoyant hydrothermal plume particulate samples collected above the TAG vent field. Quantitative removal of vent fluid derived REE, with the possible exception of Eu, during buoyant plume rise means that hydrothermal activity has no direct impact on the seawater chemistry of the REE. If coprecipitation and scavenging within the TAG hydrothermal plume are typical, such processes during plume rise and dispersion play a significant role in the removal of reactive trace metals and oxyanions from seawater, at rates of the same order as those of river input to the oceans. 51 refs., 11 figs., 7 tabs.

  20. The Effect of an Externally Attached Neutrally Buoyant Transmitter on Mortal Injury during Simulated Hydroturbine Passage

    SciTech Connect

    Brown, Richard S.; Pflugrath, Brett D.; Carlson, Thomas J.; Deng, Zhiqun

    2012-02-03

    On their seaward migration, juvenile salmonids commonly pass hydroelectric dams. Fish passing through hydroturbines experience a rapid decrease in pressure as they pass by the turbine blade and the severity of this decompression can be highly variable. This rapid decrease in pressure can result in injuries such as swim bladder rupture, exophthalmia, and emboli and hemorrhaging in the fins and tissues. However, recent research indicates that the presence of a telemetry tag (acoustic, radio, inductive) implanted inside the coelom of a juvenile salmon increases the likelihood that the fish will be injured or die during turbine passage. Thus, previous research conducted using telemetry tags implanted into the coelom of fish may have been inaccurate. Thus, a new technique is needed to provide unbiased estimates of survival through turbines. This research provides an evaluation of the effectiveness of a neutrally buoyant externally attached acoustic transmitter. Both nontagged fish and fish tagged with a neutrally buoyant external transmitter were exposed to a range of rapid decompressions simulating turbine passage. Juvenile Chinook salmon tagged with a neutrally buoyant externally attached acoustic transmitter did not receive a higher degree of barotrauma than their nontagged counterparts. We suggest that future research include field-based comparisons of survival and behavior among fish tagged with a neutrally buoyant external transmitter and those internally implanted with transmitters.

  1. 46 CFR 180.137 - Stowage of life floats and buoyant apparatus.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 7 2010-10-01 2010-10-01 false Stowage of life floats and buoyant apparatus. 180.137 Section 180.137 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) SMALL PASSENGER VESSELS (UNDER 100 GROSS TONS) LIFESAVING EQUIPMENT AND ARRANGEMENTS Survival Craft Arrangements and Equipment § 180.137 Stowage of life floats...

  2. Effect of Technology Enhanced Conceptual Change Texts on Students' Understanding of Buoyant Force

    ERIC Educational Resources Information Center

    Ozkan, Gulbin; Selcuk, Gamze Sezgin

    2015-01-01

    In this study, the effect of technology enhanced conceptual change texts on elementary school students' understanding of buoyant force was investigated. The conceptual change texts (written forms) used in this study are proven for effectiveness and are enriched by using technology support in this study. These texts were tried out on two groups. A…

  3. 46 CFR 122.730 - Servicing of inflatable liferafts, inflatable buoyant apparatus, inflatable life jackets, and...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Inspection of Lifesaving Equipment § 122.730 Servicing of inflatable liferafts, inflatable buoyant apparatus... apparatus must be serviced at a facility specifically approved by the Commandant for the particular brand... apparatus, inflatable life jackets, and inflated rescue boats. 122.730 Section 122.730 Shipping COAST...

  4. 46 CFR 185.730 - Servicing of inflatable liferafts, inflatable buoyant apparatus, inflatable life jackets, and...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... inflatable liferaft or inflatable buoyant apparatus must be serviced at a facility specifically approved by... apparatus, inflatable life jackets, and inflated rescue boats. 185.730 Section 185.730 Shipping COAST GUARD... Operational Readiness, Maintenance, and Inspection of Lifesaving Equipment § 185.730 Servicing of...

  5. 46 CFR 122.730 - Servicing of inflatable liferafts, inflatable buoyant apparatus, inflatable life jackets, and...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Inspection of Lifesaving Equipment § 122.730 Servicing of inflatable liferafts, inflatable buoyant apparatus... apparatus must be serviced at a facility specifically approved by the Commandant for the particular brand... apparatus, inflatable life jackets, and inflated rescue boats. 122.730 Section 122.730 Shipping COAST...

  6. 46 CFR 185.730 - Servicing of inflatable liferafts, inflatable buoyant apparatus, inflatable life jackets, and...

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... inflatable liferaft or inflatable buoyant apparatus must be serviced at a facility specifically approved by... apparatus, inflatable life jackets, and inflated rescue boats. 185.730 Section 185.730 Shipping COAST GUARD... Operational Readiness, Maintenance, and Inspection of Lifesaving Equipment § 185.730 Servicing of...

  7. A study of the accuracy of neutrally buoyant bubbles used as flow tracers in air

    NASA Technical Reports Server (NTRS)

    Kerho, Michael F.

    1993-01-01

    Research has been performed to determine the accuracy of neutrally buoyant and near neutrally buoyant bubbles used as flow tracers in air. Theoretical, computational, and experimental results are presented to evaluate the dynamics of bubble trajectories and factors affecting their ability to trace flow-field streamlines. The equation of motion for a single bubble was obtained and evaluated using a computational scheme to determine the factors which affect a bubble's trajectory. A two-dimensional experiment was also conducted to experimentally determine bubble trajectories in the stagnation region of NACA 0012 airfoil at 0 deg angle of attack using a commercially available helium bubble generation system. Physical properties of the experimental bubble trajectories were estimated using the computational scheme. These properties included the density ratio and diameter of the individual bubbles. the helium bubble system was then used to visualize and document the flow field about a 30 deg swept semispan wing with simulated glaze ice. Results were compared to Navier-Stokes calculations and surface oil flow visualization. The theoretical and computational analysis have shown that neutrally buoyant bubbles will trace even the most complex flow patterns. Experimental analysis revealed that the use of bubbles to trace flow patterns should be limited to qualitative measurements unless care is taken to ensure neutral buoyancy. This is due to the difficulty in the production of neutrally buoyant bubbles.

  8. Applying a Predict-Observe-Explain Sequence in Teaching of Buoyant Force

    ERIC Educational Resources Information Center

    Radovanovic, Jelena; Slisko, Josip

    2013-01-01

    An active learning sequence based on the predict-observe-explain teaching strategy is applied to a lesson on buoyant force. The results obtained clearly justify the use of this teaching method and suggest devising a series of activities to enable more effective removal of students' commonly held alternative conceptions regarding floating and…

  9. 3D Numerical Simulation of Turbulent Buoyant Flow and Heat Transport in a Curved Open Channel

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A three-dimensional buoyancy-extended version of kappa-epsilon turbulence model was developed for simulating the turbulent flow and heat transport in a curved open channel. The density- induced buoyant force was included in the model, and the influence of temperature stratification on flow field was...

  10. BUOYANT PLUME DISPERSAL IN THE CONVECTIVE BOUNDARY LAYER: ANALYSIS OF EXPERIMENTAL DATA AND LAGRANGIAN MODELING

    EPA Science Inventory

    The aim of this research program is to improve our knowledge and predictive capability of buoyant plume dispersion in the convective boundary layer (CBL) with emphasis on the mean (C) and root-mean-square (?c) concentration fields. The CBL turbulence leads to large random fluc...

  11. The influence of shelfbreak forcing on the alongshelf penetration of the Danube buoyant water, Black sea

    NASA Astrophysics Data System (ADS)

    Yankovsky, Alexander E.; Lemeshko, Evgeny M.; Ilyin, Yuriy P.

    2004-06-01

    The buoyancy-driven coastal current propagating along the western coast in the Black Sea is forced by the discharge of several major European rivers including the Danube, Dnepr and South Bug. In this study, we present observational evidence that the buoyant water alongshelf penetration is strongly affected by shelfbreak mesoscale features associated with the Rim Current dynamics. The Rim Current is a major element of the Black Sea general circulation, typically following isobaths over the upper-to-middle slope. Two hydrographic surveys conducted in 1992 and 1994 have been chosen among available archive data for the detailed analysis. In both years, though Danube buoyant discharge was similar prior to the beginning of shipboard observations (varying around 7000 m 3 s -1), the buoyant water exhibited very different downstream (that is, in the direction of Kelvin wave) penetration. In 1992, it spread all the way around the southwestern corner of the Black Sea basin and then further eastward past the Bosporus Strait. In contrast, its downstream penetration was blocked in 1994 and buoyant water did not even reach Cape Kaliakra on the Bulgarian coast. This difference was related to the shelfbreak processes. In 1992, the cyclonic meander of the Rim Current merged with the coastal buoyant water thus promoting its advection from Cape Kaliakra downstream. In 1994, a strong anticyclone in the southwestern corner of the Black Sea completely blocked the propagation of a buoyancy-driven current past Cape Kaliakra. In addition, another anticyclone in the northwestern part of the sea advected buoyant water offshore to the central area of the northwestern shelf. The positions of anticyclonic eddies during a period of observations was confirmed by remote sensing data. As these and other examples indicate, coastal buoyancy driven currents can be effectively blocked and dispersed offshore by the shelfbreak anticyclones if the shelf width allows their interaction with buoyant water

  12. Migration of buoyant non-wetting fluids in heterogeneous porous media

    NASA Astrophysics Data System (ADS)

    Huber, C.; Parmigiani, A.; Faroughi, S. A.; Bachmann, O.; Karani, H.

    2015-12-01

    The buoyant migration of a non-wetting fluid in porous media occurs in several natural contexts, such as during CO2 sequestration, methane in cold seeps, DNAPLs infiltration in groundwater, oil recovery and magma chambers. In this study, we use numerical modeling and laboratory experiments to investigate the migration of buoyant non-wetting fluids in time-dependent (reactive) or spatially heterogeneous porous media. We find that the stress balance at the pore scale greatly influences the migration dynamics and regime of viscous energy dissipation of the flow (low Re) and therefore impacts the transport of non-wetting fluid even at the field scale. We consider two complementary pore-scale studies. In the first case, the migration of the non-wetting fluid is impacted by the concurrent dissolution of the porous medium because of the reactivity of the buoyant invading fluid. In the second scenario a chemically inert buoyant non-wetting fluid migrates across an heterogeneous medium, from a low porosity (and permeability) layer into a high porosity (high permeability) layer. We find that these two cases lead to a similar and counter-intuitive outcome: the migration of the buoyant non-wetting fluid is reduced at high porosity/permeability. These counter-intuitive results stem from the effect of confinement of the non-wetting fluid (volume available for invasion) and viscosity ratio between the immiscible fluids on the fluid migration at the pore scale. An important solid confinement (low porosity) stabilizes fingering pathways and promotes efficient transport, while high porosity promotes the formation of an emulsion with discrete bubbles or slugs of non-wetting fluids.

  13. Subduction of a buoyant plateau at the Manila Trench: Tomographic evidence and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Fan, Jianke; Zhao, Dapeng; Dong, Dongdong

    2016-02-01

    We determined P-wave tomographic images by inverting a large number of arrival-time data from 2749 local earthquakes and 1462 teleseismic events, which are used to depict the three-dimensional morphology of the subducted Eurasian Plate along the northern segment of the Manila Trench. Dramatic changes in the dip angle of the subducted Eurasian Plate are revealed from the north to the south, being consistent with the partial subduction of a buoyant plateau beneath the Luzon Arc. Slab tears may exist along the edges of the buoyant plateau within the subducted plate induced by the plateau subduction, and the subducted lithosphere may be absent at depths greater than 250 km at ˜19°N and ˜21°N. The subducted buoyant plateau is possibly oriented toward NW-SE, and the subducted plate at ˜21°N is slightly steeper than that at ˜19°N. These results may explain why the western and eastern volcanic chains in the Luzon Arc are separated by ˜50 km at ˜18°N, whereas they converge into a single volcanic chain northward, which may be related to the oblique subduction along the Manila Trench caused by the northwestern movement of the Philippine Sea Plate. A low-velocity zone is revealed at depths of 20-200 km beneath the Manila Accretionary Prism at ˜22°N, suggesting that the subduction along the Manila Trench may stop there and the collision develops northward. The Taiwan Orogeny may originate directly from the subduction of the buoyant plateau, because the initial time of the Taiwan Orogeny is coincident with that of the buoyant plateau subduction.

  14. Smoke-Point Properties of Non-Buoyant Round Laminar Jet Diffusion Flames. Appendix J

    NASA Technical Reports Server (NTRS)

    Urban, D. L.; Yuan, Z.-G.; Sunderland, P. B.; Lin, K.-C.; Dai, Z.; Faeth, G. M.

    2000-01-01

    The laminar smoke-point properties of non-buoyant round laminar jet diffusion flames were studied emphasizing results from long-duration (100-230 s) experiments at microgravity carried out in orbit aboard the space shuttle Columbia. Experimental conditions included ethylene- and propane-fueled flames burning in still air at an ambient temperature of 300 K, pressures of 35-130 kPa, jet exit diameters of 1.6 and 2.7 mm, jet exit velocities of 170-690 mm/s, jet exit Reynolds numbers of 46-172, characteristic flame residence times of 40-302 ms, and luminous flame lengths of 15-63 mm. Contrary to the normal-gravity laminar smoke point, in microgravity, the onset of laminar smoke-point conditions involved two flame configurations: closed-tip flames with soot emissions along the flame axis and open-tip flames with soot emissions from an annular ring about the flame axis. Open-tip flames were observed at large characteristic flame residence times with the onset of soot emissions associated with radiative quenching near the flame tip: nevertheless, unified correlations of laminar smoke-point properties were obtained that included both flame configurations. Flame lengths at laminar smoke-point conditions were well correlated in terms of a corrected fuel flow rate suggested by a simplified analysis of flame shape. The present steady and non-buoyant flames emitted soot more readily than non-buoyant flames in earlier tests using ground-based microgravity facilities and than buoyant flames at normal gravity, as a result of reduced effects of unsteadiness, flame disturbances, and buoyant motion. For example, present measurements of laminar smoke-point flame lengths at comparable conditions were up to 2.3 times shorter than ground-based microgravity measurements and up to 6.4 times shorter than buoyant flame measurements. Finally, present laminar smoke-point flame lengths were roughly inversely proportional to pressure to a degree that is a somewhat smaller than observed during

  15. Wake-Driven Dynamics of Finite-Sized Buoyant Spheres in Turbulence.

    PubMed

    Mathai, Varghese; Prakash, Vivek N; Brons, Jon; Sun, Chao; Lohse, Detlef

    2015-09-18

    Particles suspended in turbulent flows are affected by the turbulence and at the same time act back on the flow. The resulting coupling can give rise to rich variability in their dynamics. Here we report experimental results from an investigation of finite-sized buoyant spheres in turbulence. We find that even a marginal reduction in the particle's density from that of the fluid can result in strong modification of its dynamics. In contrast to classical spatial filtering arguments and predictions of particle models, we find that the particle acceleration variance increases with size. We trace this reversed trend back to the growing contribution from wake-induced forces, unaccounted for in current particle models in turbulence. Our findings highlight the need for improved multiphysics based models that account for particle wake effects for a faithful representation of buoyant-sphere dynamics in turbulence. PMID:26430995

  16. The shape and behaviour of a horizontal buoyant jet adjacent to a surface

    NASA Astrophysics Data System (ADS)

    Burridge, Henry; Hunt, Gary

    2015-11-01

    We investigate the incompressible turbulent buoyant jet formed when fluid is steadily ejected horizontally from a circular source into a quiescent environment of uniform density. As our primary focus, we introduce a horizontal boundary. For sufficiently large source-boundary separations, the buoyant jet is `free' to rise under the action of the buoyancy force. For smaller source-boundary separations, the jet attaches and `clings' to the boundary before, further downstream, pulling away from the boundary. Based on measurements of saline jets in freshwater we deduce the conditions required for a jet to cling. We present data for the variation in volume flux, flow envelope and centreline for both `clinging' and `free' jets. For source Froude numbers fr0 >= 12 the data collapses when scaled, identifying universal behaviours for both clinging jets and for free jets. The support and funding from Dyson Technology Ltd is gratefully acknowledged.

  17. A buoyant plume adjacent to a headland—Observations of the Elwha River plume

    NASA Astrophysics Data System (ADS)

    Warrick, Jonathan A.; Stevens, Andrew W.

    2011-02-01

    Small rivers commonly discharge into coastal settings with topographic complexities - such as headlands and islands - but these settings are underrepresented in river plume studies compared to more simplified, straight coasts. The Elwha River provides a unique opportunity to study the effects of coastal topography on a buoyant plume, because it discharges into the Strait of Juan de Fuca on the western side of its deltaic headland. Here we show that this headland induces flow separation and transient eddies in the tidally dominated currents (O(100 cm/s)), consistent with other headlands in oscillatory flow. These flow conditions are observed to strongly influence the buoyant river plume, as predicted by the “small-scale” or “narrow” dynamical classification using Garvine's (1995) system. Because of the transient eddies and the location of the river mouth on the headland, flow immediately offshore of the river mouth is directed eastward twice as frequently as it is westward. This results in a buoyant plume that is much more frequently “bent over” toward the east than the west. During bent over plume conditions, the plume was attached to the eastern shoreline while having a distinct, cuspate front along its westernmost boundary. The location of the front was found to be related to the magnitude and direction of local flow during the preceding O(1 h), and increases in alongshore flow resulted in deeper freshwater mixing, stronger baroclinic anomalies, and stronger hugging of the coast. During bent over plume conditions, we observed significant convergence of river plume water toward the frontal boundary within 1 km of the river mouth. These results show how coastal topography can strongly influence buoyant plume behavior, and they should assist with understanding of initial coastal sediment dispersal pathways from the Elwha River during a pending dam removal project.

  18. A buoyant plume adjacent to a headland-Observations of the Elwha River plume

    USGS Publications Warehouse

    Warrick, J.A.; Stevens, A.W.

    2011-01-01

    Small rivers commonly discharge into coastal settings with topographic complexities - such as headlands and islands - but these settings are underrepresented in river plume studies compared to more simplified, straight coasts. The Elwha River provides a unique opportunity to study the effects of coastal topography on a buoyant plume, because it discharges into the Strait of Juan de Fuca on the western side of its deltaic headland. Here we show that this headland induces flow separation and transient eddies in the tidally dominated currents (O(100. cm/s)), consistent with other headlands in oscillatory flow. These flow conditions are observed to strongly influence the buoyant river plume, as predicted by the "small-scale" or "narrow" dynamical classification using Garvine's (1995) system. Because of the transient eddies and the location of the river mouth on the headland, flow immediately offshore of the river mouth is directed eastward twice as frequently as it is westward. This results in a buoyant plume that is much more frequently "bent over" toward the east than the west. During bent over plume conditions, the plume was attached to the eastern shoreline while having a distinct, cuspate front along its westernmost boundary. The location of the front was found to be related to the magnitude and direction of local flow during the preceding O(1. h), and increases in alongshore flow resulted in deeper freshwater mixing, stronger baroclinic anomalies, and stronger hugging of the coast. During bent over plume conditions, we observed significant convergence of river plume water toward the frontal boundary within 1. km of the river mouth. These results show how coastal topography can strongly influence buoyant plume behavior, and they should assist with understanding of initial coastal sediment dispersal pathways from the Elwha River during a pending dam removal project. ?? 2010.

  19. On the Alignment of Strain, Vorticity and Scalar Gradient in Turbulent, Buoyant, Nonpremixed Flames

    NASA Technical Reports Server (NTRS)

    Boratav, O. N.; Elghobashi, S. E.; Zhong, R.

    1999-01-01

    The alignment of vorticity and scalar gradient with the eigendirections of the rate of strain tensor is investigated in turbulent buoyant nonpremixed horizontal and vertical flames. The uniqueness of a buoyant nonpremixed flame is that it contains regions with distinct alignment characteristics. The strain-enstrophy angle Psi is used to identify these regions. Examination of the vorticity field and the vorticity production in these different regions indicates that Psi and consequently the alignment properties near the flame surface identified by the mixture fraction band F approximately equals F(sub st) differ from those in the fuel region, F > F(sub st) and the oxidizer region, F < F(sub st). The F approximately equals F(sub st) band shows strain-dominance resulting in vorticity/alpha alignment while F > F(sub st) (and F < F(sub st) for the vertical flame) band(s) show(s) vorticity/beta alignment. The implication of this result is that the scalar dissipation, epsilon(sub F), attains its maximum value always near F approximately equals F(sub st). These results are also discussed within the framework of recent dynamical results [Galanti et al., Nonlinearity 10, 1675 (1997)] suggesting that the Navier-Stokes equations evolved towards an attracting solution. It is shown that the properties of such an attracting solution are also consistent with our results of buoyant turbulent nonpremixed flames.

  20. Buoyant Magnetic Loops in a Global Dynamo Simulation of a Young Sun

    NASA Astrophysics Data System (ADS)

    Nelson, Nicholas J.; Brown, Benjamin P.; Brun, Allan Sacha; Miesch, Mark S.; Toomre, Juri

    2011-10-01

    The current dynamo paradigm for the Sun and Sun-like stars places the generation site for strong toroidal magnetic structures deep in the solar interior. Sunspots and starspots on Sun-like stars are believed to arise when sections of these magnetic structures become buoyantly unstable and rise from the deep interior to the photosphere. Here, we present the first three-dimensional global magnetohydrodynamic (MHD) simulation in which turbulent convection, stratification, and rotation combine to yield a dynamo that self-consistently generates buoyant magnetic loops. We simulate stellar convection and dynamo action in a spherical shell with solar stratification, but rotating three times faster than the current solar rate. Strong wreaths of toroidal magnetic field are realized by dynamo action in the convection zone. By turning to a dynamic Smagorinsky model for subgrid-scale turbulence, we here attain considerably reduced diffusion in our simulation. This permits the regions of strongest magnetic field in these wreaths to rise toward the top of the convection zone via a combination of magnetic buoyancy instabilities and advection by convective giant cells. Such a global simulation yielding buoyant loops represents a significant step forward in combining numerical models of dynamo action and flux emergence.

  1. Effect of inlet conditions on the turbulent statistics in a buoyant jet

    NASA Astrophysics Data System (ADS)

    Kumar, Rajesh; Dewan, Anupam

    2015-11-01

    Buoyant jets have been the subject of research due to their technological and environmental importance in many physical processes, such as, spread of smoke and toxic gases from fires, release of gases form volcanic eruptions and industrial stacks. The nature of the flow near the source is initially laminar which quickly changes into turbulent flow. We present large eddy simulation of a buoyant jet. In the present study a careful investigation has been done to study the influence of inlet conditions at the source on the turbulent statistics far from the source. It has been observed that the influence of the initial conditions on the second-order buoyancy terms extends further in the axial direction from the source than their influence on the time-averaged flow and second-order velocity statistics. We have studied the evolution of vortical structures in the buoyant jet. It has been shown that the generation of helical vortex rings in the vicinity of the source around a laminar core could be the reason for the larger influence of the inlet conditions on the second-order buoyancy terms as compared to the second-order velocity statistics.

  2. Influence of Buoyant Convection on the Stability of Enclosed Laminar Flames

    NASA Technical Reports Server (NTRS)

    Brooker, John E.; Jia, Kezhong; Stocker, Dennis P.; Chen. Lea-Der

    1999-01-01

    Enclosed diffusion flames are commonly found in practical combustion systems, such as the power-plant combustor, gas turbine combustor, and jet engine after-burner. In these systems, fuel is injected into a duct with a co-flowing or cross-flowing air stream. In combustors, this flame is anchored at the burner (i.e., fuel jet inlet) unless adverse conditions cause the flame to lift off or blow out. Investigations of burner stability study the lift off, reattachment, and blow out of the flame. There have been numerous studies of flame stability. Relatively few studies have investigated the stability of flames with an oxidizer co-flow, compared with the number of studies on (nearly) free jet diffusion flames. The air flow around the fuel jet can significantly alter the lift off, reattachment and blow out of the jet diffusion flame. In normal gravity, however, the effects of the air flow on flame stability are often complicated by the presence of buoyant convection. A comparison of normal-gravity and microgravity flames can provide clear indication of the influence of forced and buoyant flows on the flame stability. The overall goal of the Enclosed Laminar Flames (ELF) research, described at the following URL site: http://zeta.lerc.nasa.gov/expr/elf.htm, is to improve our understanding of the effects of buoyant convection on the structure and stability of co-flow diffusion flames.

  3. BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN

    SciTech Connect

    Nelson, Nicholas J.; Toomre, Juri; Brown, Benjamin P.; Brun, Allan Sacha

    2011-10-01

    The current dynamo paradigm for the Sun and Sun-like stars places the generation site for strong toroidal magnetic structures deep in the solar interior. Sunspots and starspots on Sun-like stars are believed to arise when sections of these magnetic structures become buoyantly unstable and rise from the deep interior to the photosphere. Here, we present the first three-dimensional global magnetohydrodynamic (MHD) simulation in which turbulent convection, stratification, and rotation combine to yield a dynamo that self-consistently generates buoyant magnetic loops. We simulate stellar convection and dynamo action in a spherical shell with solar stratification, but rotating three times faster than the current solar rate. Strong wreaths of toroidal magnetic field are realized by dynamo action in the convection zone. By turning to a dynamic Smagorinsky model for subgrid-scale turbulence, we here attain considerably reduced diffusion in our simulation. This permits the regions of strongest magnetic field in these wreaths to rise toward the top of the convection zone via a combination of magnetic buoyancy instabilities and advection by convective giant cells. Such a global simulation yielding buoyant loops represents a significant step forward in combining numerical models of dynamo action and flux emergence.

  4. Early-stage hypogene karstification in a mountain hydrologic system: A coupled thermohydrochemical model incorporating buoyant convection

    NASA Astrophysics Data System (ADS)

    Chaudhuri, A.; Rajaram, H.; Viswanathan, H.

    2013-09-01

    The early stage of hypogene karstification is investigated using a coupled thermohydrochemical model of a mountain hydrologic system, in which water enters along a water table and descends to significant depth (˜1 km) before ascending through a central high-permeability fracture. The model incorporates reactive alteration driven by dissolution/precipitation of limestone in a carbonic acid system, due to both temperature- and pressure-dependent solubility, and kinetics. Simulations were carried out for homogeneous and heterogeneous initial fracture aperture fields, using the FEHM (Finite Element Heat and Mass Transfer) code. Initially, retrograde solubility is the dominant mechanism of fracture aperture growth. As the fracture transmissivity increases, a critical Rayleigh number value is exceeded at some stage. Buoyant convection is then initiated and controls the evolution of the system thereafter. For an initially homogeneous fracture aperture field, deep well-organized buoyant convection rolls form. For initially heterogeneous aperture fields, preferential flow suppresses large buoyant convection rolls, although a large number of smaller rolls form. Even after the onset of buoyant convection, dissolution in the fracture is sustained along upward flow paths by retrograde solubility and by additional "mixing corrosion" effects closer to the surface. Aperture growth patterns in the fracture are very different from those observed in simulations of epigenic karst systems, and retain imprints of both buoyant convection and preferential flow. Both retrograde solubility and buoyant convection contribute to these differences. The paper demonstrates the potential value of coupled models as tools for understanding the evolution and behavior of hypogene karst systems.

  5. Small dense LDL is more susceptible to glycation than more buoyant LDL in Type 2 diabetes.

    PubMed

    Younis, Nahla N; Soran, Handrean; Pemberton, Philip; Charlton-Menys, Valentine; Elseweidy, Mohamed M; Durrington, Paul N

    2013-03-01

    Glycation of apoB (apolipoprotein B) of LDL (low-density lipoprotein) increases its atherogenicity. Concentrations of both serum glyc-apoB (glycated apoB) and SD-LDL (small dense LDL) (syn LDL3; D=1.044-1.063 g/ml) are increased in diabetes and are closely correlated. We studied whether SD-LDL is more susceptible to glycation in vitro than more buoyant LDL in statin- and non-statin-treated Type 2 diabetes mellitus. Serum SD-LDL apoB and glyc-apoB on statins was 20±2 (means±S.D.) and 3.6±0.41 compared with 47±3 and 5.89±0.68 mg/dl in those not receiving statins (P<0.001 and <0.01, respectively). There was a dose-dependent increase in glycation on incubation of LDL subfractions with glucose, which was accompanied by an increase in LPO (lipid peroxide) and electrophoretic mobility and a decrease in free amino groups. SD-LDL was more susceptible to these changes than more buoyant LDL. Both SD-LDL and more buoyant LDL from statin-treated patients were less susceptible to glycation. There were fewer free amino groups on LDL subfractions from statin-treated patients, which may contribute to this resistance. In conclusion, greater susceptibility of SD-LDL to glycation is likely to contribute to the raised levels of circulating glyc-apoB in diabetes. Statins are associated with lower levels of both SD-LDL and glyc-apoB. PMID:22985435

  6. Buoyant Turbulence Kinetic Energy (TKE) Production in Katabatic Flow Despite Stable Thermal Stratification

    NASA Astrophysics Data System (ADS)

    Oldroyd, H. J.; Pardyjak, E.; Higgins, C. W.; Parlange, M. B.

    2015-12-01

    As micrometeorological research shifts to increasingly non-idealized environments, the lens through which we view classical atmospheric boundary layer theory must also shift to accommodate unfamiliar behavior. We present observations of katabatic flow over a steep (35.5 degree), alpine slope and draw comparisons with classical theory for nocturnal boundary layers (NBL) over flat terrain to delineate key physical differences and similarities. In both cases, the NBL is characterized by a strong, terrain-aligned thermal stratification. Over flat terrain, this temperature inversion tends to stabilize perturbations and suppresses vertical motions. Hence, the buoyancy term in the TKE budget equation acts as a sink. In contrast, the steep-slope katabatic flow regime is characterized by buoyant TKE production despite NBL thermal stratification. This buoyant TKE production occurs because streamwise (upslope) heat fluxes, which are typically treated as unimportant over flat terrain, contribute to the total vertical buoyancy flux since the gravity vector is not terrain-normal. Due to a relatively small number of observations over steep terrain, the turbulence structure of such flows and the implications of buoyant TKE production in the NBL have gone largely unexplored. As an important consequence of this characteristic, we show that conventional stability characterizations require careful coordinate system alignment and interpretation for katabatic flows. The streamwise heat fluxes play an integral role in characterizing stability and turbulent transport, more broadly, in katabatic flows. Therefore, multi-scale statistics and budget analyses describing physical interactions between turbulent fluxes at various scales are presented to interpret similarities and differences between the observations and classical theories regarding streamwise heat fluxes.

  7. Large Eddy Simulation of a Forced Round Turbulent Buoyant Plume in Neutral Surroundings

    NASA Technical Reports Server (NTRS)

    Basu, A. J.; Mansour, N. N.; Koga, Dennis (Technical Monitor)

    1999-01-01

    Buoyant flows play an important role in various technological and environmental issues. For example, dispersal of pollutants, smoke, or volcano exhaust in the atmosphere, vertical motion of air, formation of clouds and other weather systems, and flows in cooling towers and fires are all determined primarily by buoyancy effects. The buoyancy force in such flows can originate from either a heat source or due to different densities between a fluid and its surroundings. Whatever the cause, the flow can be understood by studying the effects of the tight coupling between the thermal and the velocity fields since density differences can be characterized as temperature differences.

  8. Three-Dimensional Magnetohydrodynamic Simulations of Buoyant Bubbles in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    O'Neill, Sean M.; De Young, David S.; Jones, Thomas W.

    2009-12-01

    We present the results of numerical models of bubble dynamics and morphology in magnetized galaxy cluster environments. Our set of simulations follows the evolution of initially spherical bubbles that rise buoyantly through the intracluster medium. As a result of commonly used initial conditions, such bubbles quickly develop into a toroidal shape that is stable against fragmentation in the absence of magnetic forces. The inclusion of even modest ambient magnetic fields, however, substantially affects such structures, and we discuss how bubble evolution depends upon ambient field strength and geometry.

  9. Detection of a buoyant coastal wastewater discharge using airborne hyperspectral and infrared imagery

    NASA Astrophysics Data System (ADS)

    Marmorino, George O.; Smith, Geoffrey B.; Miller, W. D.; Bowles, Jeffrey H.

    2010-01-01

    Municipal wastewater discharged into the ocean through a submerged pipe, or outfall, can rise buoyantly to the sea surface, resulting in a near-field mixing zone and, in the presence of an ambient ocean current, an extended surface plume. In this paper, data from a CASI (Compact Airborne Spectrographic Imager) and an airborne infrared (IR) camera are shown to detect a municipal wastewater discharge off the southeast coast of Florida, U.S.A., through its elevated levels of chromophoric dissolved organic matter plus detrital material (CDOM) and cooler sea surface temperatures. CDOM levels within a ~15-m-diameter surface 'boil' are found to be about twice those in the ambient shelf water, and surface temperatures near the boil are lower by ~0.4°C, comparable to the vertical temperature difference across the ambient water column. The CASI and IR imagery show a nearly identically shaped buoyant plume, consistent with a fully surfacing discharge, but the IR data more accurately delineate the area of most rapid dilution as compared with previous in-situ measurements. The imagery also allows identification of ambient oceanographic processes that affect dispersion and transport in the far field. This includes an alongshore front, which limits offshore dispersion of the discharge, and shoreward-propagating nonlinear internal waves, which may be responsible for an enhanced onshore transport of the discharge.

  10. Beauty of lotus is more than skin deep: highly buoyant superhydrophobic films.

    PubMed

    Choi, Yuri; Brugarolas, Teresa; Kang, Sung-Min; Park, Bum Jun; Kim, Byeong-Su; Lee, Chang-Soo; Lee, Daeyeon

    2014-05-28

    We develop highly buoyant superhydrophobic films that mimic the three-dimensional structure of lotus leaves. The high buoyancy of these structure stems from mechanically robust bubbles that significantly reduce the density of the superhydrophobic films. These highly buoyant superhydrophobic films stay afloat on water surface while carrying a load that is more than 200 times their own weight. In addition to imparting high buoyancy, the incorporation of robust hydrophilic bubbles enables the formation of free-standing structures that mimic the water-collection properties of Namib Desert beetle. We believe the incorporation of robust bubbles is a general method that opens up numerous possibilities in imparting high buoyancy to different structures that needs to stay afloat on water surfaces and can potentially be used for the fabrication of lightweight materials. (Image on the upper left reproduced with permission from Yong, J.; Yang, Q.; Chen, F.; Zhang, D.; Du, G.; Si, J.; Yun, F.; Hou, X. A Bioinspired Planar Superhydrophobic Microboat. J. Micromech. Microeng. 2014, 24, 035006). PMID:24801001

  11. Dense nanoparticles exhibit enhanced vascular wall targeting over neutrally buoyant nanoparticles in human blood flow.

    PubMed

    Thompson, Alex J; Eniola-Adefeso, Omolola

    2015-07-01

    For vascular-targeting carrier (VTC) systems to be effective, carriers must be able to localize and adhere to the vascular wall at the target site. Research suggests that neutrally buoyant nanoparticles are limited by their inability to localize to the endothelium, making them sub-optimal as carriers. This study examines whether particle density can be exploited to improve the targeting (localization and adhesion) efficiency of nanospheres to the vasculature. Silica spheres with 500 nm diameter, which have a density roughly twice that of blood, exhibit improved adhesion to inflamed endothelium in an in vitro model of human vasculature compared to neutrally buoyant polystyrene spheres of the same size. Silica spheres also display better near-wall localization in the presence of red blood cells than they do in pure buffer, likely resulting in the observed improvement in adhesion. Titania spheres (4 times more dense than blood) adhere at levels higher than polystyrene, but only in conditions when gravity or centrifugal force acts in the direction of adhesion. In light of the wide array of materials proposed for use as carrier systems for drug delivery and diagnostics, particle density may be a useful tool for improving the targeting of diseased tissues. PMID:25870170

  12. Experimental investigation of steady buoyant-thermocapillary convection near an evaporating meniscus

    NASA Astrophysics Data System (ADS)

    Dhavaleswarapu, Hemanth K.; Chamarthy, Pramod; Garimella, Suresh V.; Murthy, Jayathi Y.

    2007-08-01

    Micro-particle image velocimetry measurements of the three-dimensional (3D) convection patterns generated near an evaporating meniscus in horizontally oriented capillary tubes are presented. Analysis of the vapor diffusion away from the meniscus reveals a zone of intense heat flux near the solid-liquid-vapor junction that creates a temperature gradient along the meniscus. This results in a surface tension gradient which, coupled with buoyancy effects, causes buoyant-thermocapillary convection in the liquid film. The relative influence of buoyancy and thermocapillarity on the flow was investigated for tube diameters ranging from 75 to 1575μm. A transition from a pure two-dimensional thermocapillary flow to a 3D buoyant-thermocapillary flow is observed with an increase in tube diameter. For the 75μm tube, a symmetrical toroidal vortex is observed near the meniscus. For larger tubes, buoyancy effects become apparent as they dominate the flow field. The high mass fluxes in smaller-diameter tubes drive stronger vortices. Particle streaks and micro-particle image velocimetry images obtained in multiple horizontal and vertical planes provide an understanding of this three-dimensional flow behavior. A scaling analysis shows the importance of thermocapillary convection in evaporating menisci.

  13. Estimating the neutrally buoyant energy density of a Rankine-cycle/fuel-cell underwater propulsion system

    NASA Astrophysics Data System (ADS)

    Waters, Daniel F.; Cadou, Christopher P.

    2014-02-01

    A unique requirement of underwater vehicles' power/energy systems is that they remain neutrally buoyant over the course of a mission. Previous work published in the Journal of Power Sources reported gross as opposed to neutrally-buoyant energy densities of an integrated solid oxide fuel cell/Rankine-cycle based power system based on the exothermic reaction of aluminum with seawater. This paper corrects this shortcoming by presenting a model for estimating system mass and using it to update the key findings of the original paper in the context of the neutral buoyancy requirement. It also presents an expanded sensitivity analysis to illustrate the influence of various design and modeling assumptions. While energy density is very sensitive to turbine efficiency (sensitivity coefficient in excess of 0.60), it is relatively insensitive to all other major design parameters (sensitivity coefficients < 0.15) like compressor efficiency, inlet water temperature, scaling methodology, etc. The neutral buoyancy requirement introduces a significant (˜15%) energy density penalty but overall the system still appears to offer factors of five to eight improvements in energy density (i.e., vehicle range/endurance) over present battery-based technologies.

  14. Saltwater intrusion at a buoyant jet discharge in a fringing reef lagoon

    NASA Astrophysics Data System (ADS)

    Parra, S. M.; Marino-Tapia, I.; Enriquez, C.; Valle-Levinson, A.

    2013-05-01

    The influence of tides and waves on turbulent kinetic energy (TKE) from a buoyant jet discharge in a fringing reef lagoon was observed with measurements obtained throughout an 11-day period in July 2011. Tidal variations within the lagoon modulated TKE levels, temperature, and salinity at the buoyant jet. During neap and low tides, TKE values were predominantly >0.015 m2/s2. During neap tides, TKE at the jet was greater than during spring tides, meaning that larger tidal oscillations inhibited TKE production at the jet. When the water surface over the jet remained >0.02 m above the mean, TKE was suppressed to <0.005 m2/s2. During spring and high tides, the jet reversed flow directions, for the first time showing saltwater intrusion into the aquifer. This demonstrates the sensitivity of the jet discharge to fortnightly tides, despite the small tidal range (<0.3 m during spring tide) in the study area. Additionally, wind-waves from a passing storm (occurring towards the end of the measurement period) produced greater incident waves and created a wave set-up within the lagoon. The wave set-up further stressed the jet, reinforcing the salt intrusion into the aquifer caused by the spring tide oscillations. Therefore, increased sea levels, as illustrated here by the combination of incident waves, wave set-up and fortnightly tidal oscillations, is expected to threaten delicate aquifer conditions and vital water resources for coastal communities worldwide.

  15. Particle-size distributions and their effect on entrainment in turbulent buoyant plumes

    NASA Astrophysics Data System (ADS)

    Jessop, D.; Jellinek, M.

    2014-12-01

    Explosive volcanic eruptions produce turbulent, buoyant jets that contain entrained particles. In these flows, turbulent entrainment of ambient air controls the ultimate rise height and spread of the jet. Volcanic jets are a natural example of these dilute particle-gas systems and the particles they contain can strongly control the dynamics of the bulk flow through the coupling between themselves and the surrounding fluid. The metric for the type of particle-fluid coupling is the Stokes number, St, which measures the timescale for the particles inertia against the timescale for the flow field, typically the overturn time of an eddy. We show that particles that are critically coupled to the flow (St=O(1)) change the turbulent structure of the flow by eddy stretching leading to energy cascades which are anisotropic in the horizontal and vertical directions. Crucially, flows laden with such particles carry considerably more energy in the stream-wise direction than particle-free flows which leads to a decrease in entrainment. This behaviour suggests that turbulent entrainment can effectively be shut down under critical St, giving rise to collapsing fountains whereas particle-free flows under the same source conditions would produce buoyant plumes. Changes in entrainment rates in volcanic jets are also manifested in readily observable features such as the rise height. We may therefore infer entrainment rates and their evolution over the course of an eruption from the maximum height and neutral buoyancy level.

  16. A simple technique for measuring buoyant weight increment of entire, transplanted coral colonies in the field

    PubMed Central

    Herler, Jürgen; Dirnwöber, Markus

    2011-01-01

    Estimating the impacts of global and local threats on coral reefs requires monitoring reef health and measuring coral growth and calcification rates at different time scales. This has traditionally been mostly performed in short-term experimental studies in which coral fragments were grown in the laboratory or in the field but measured ex situ. Practical techniques in which growth and measurements are performed over the long term in situ are rare. Apart from photographic approaches, weight increment measurements have also been applied. Past buoyant weight measurements under water involved a complicated and little-used apparatus. We introduce a new method that combines previous field and laboratory techniques to measure the buoyant weight of entire, transplanted corals under water. This method uses an electronic balance fitted into an acrylic glass underwater housing and placed atop of an acrylic glass cube. Within this cube, corals transplanted onto artificial bases can be attached to the balance and weighed at predetermined intervals while they continue growth in the field. We also provide a set of simple equations for the volume and weight determinations required to calculate net growth rates. The new technique is highly accurate: low error of weight determinations due to variation of coral density (< 0.08%) and low standard error (< 0.01%) for repeated measurements of the same corals. We outline a transplantation technique for properly preparing corals for such long-term in situ experiments and measurements. PMID:22049248

  17. Residence times of neutrally-buoyant matter such as larvae, sewage or nutrients on coral reefs

    NASA Astrophysics Data System (ADS)

    Black, Kerry P.; Gay, Stephen L.; Andrews, John C.

    1990-12-01

    Coral reef flushing times at an individual reef scale are specified and a general formula to determine these times is developed. The formula is confirmed by comparison with residence times predicted by numerical small-scale reef models, including those from a 4 month unsteady current simulation of John Brewer Reef on Australia's Great Barrier Reef. The method proves to be a satisfactory alternative to the numerical modelling. When neutrally-buoyant material around a reef is removed by the currents, the concentrations decay exponentially. The decay rate depends primarily on free stream current and reef dimensions. Secondary factors are the tidal excursion, shelf depth, lagoon size and residual current in the lee of the reef. These factors, when combined into a decay coefficient, specify the rate of loss of neutrally-buoyant material (e.g. some larvae, pollutants and sewage) from a coral reef and its surrounds. The analytical formula can be used to predict the flushing rates or the percentage of material still remaining on a reef after a selected time interval. We demonstrate that material can remain on or near typical reefs in common weather conditions for several weeks.

  18. Similarity theory of the buoyantly interactive planetary boundary layer with entrainment

    NASA Technical Reports Server (NTRS)

    Hoffert, M. I.; Sud, Y. C.

    1976-01-01

    A similarity model is developed for the vertical profiles of turbulent flow variables in an entraining turbulent boundary layer of arbitrary buoyant stability. In the general formulation the vertical profiles, internal rotation of the velocity vector, discontinuities or jumps at a capping inversion and bulk aerodynamic coefficients of the boundary layer are given by solutions to a system of ordinary differential equations in the similarity variable. To close the system, a formulation for buoyantly interactive eddy diffusivity in the boundary layer is introduced which recovers Monin-Obukhov similarity near the surface and incorporates a hypothesis accounting for the observed variation of mixing length throughout the boundary layer. The model is tested in simplified versions which depend only on roughness, surface buoyancy, and Coriolis effects by comparison with planetary-boundary-layer wind- and temperature-profile observations, measurements of flat-plate boundary layers in a thermally stratified wind tunnel and observations of profiles of terms in the turbulent kinetic-energy budget of convective planetary boundary layers. On balance, the simplified model reproduced the trend of these various observations and experiments reasonably well, suggesting that the full similarity formulation be pursued further.

  19. Formation of lower continental crust by relamination of buoyant arc lavas and plutons

    NASA Astrophysics Data System (ADS)

    Kelemen, Peter B.; Behn, Mark D.

    2016-03-01

    The formation of the Earth's continents is enigmatic. Volcanic arc magmas generated above subduction zones have geochemical compositions that are similar to continental crust, implying that arc magmatic processes played a central role in generating continental crust. Yet the deep crust within volcanic arcs has a very different composition from crust at similar depths beneath the continents. It is therefore unclear how arc crust is transformed into continental crust. The densest parts of arc lower crust may delaminate and become recycled into the underlying mantle. Here we show, however, that even after delamination, arc lower crust still has significantly different trace element contents from continental lower crust. We suggest that it is not delamination that determines the composition of continental crust, but relamination. In our conceptual model, buoyant magmatic rocks generated at arcs are subducted. Then, upon heating at depth, they ascend and are relaminated at the base of the overlying crust. A review of the average compositions of buoyant magmatic rocks -- lavas and plutons -- sampled from the Aleutians, Izu-Bonin-Marianas, Kohistan and Talkeetna arcs reveals that they fall within the range of estimated major and trace elements in lower continental crust. Relamination may thus provide an efficient process for generating lower continental crust.

  20. Submarine melting at tidewater glaciers: comparison of numerical modelling, buoyant plume theory and hydrographic data.

    NASA Astrophysics Data System (ADS)

    Slater, D. A.; Nienow, P. W.; Goldberg, D. N.; Cowton, T. R.; Sole, A. J.

    2014-12-01

    Observations of the mass balance of the Greenland ice sheet in recent decades have shown significant losses at the coastal margins through the thinning, speed-up and retreat of tidewater glaciers. Ocean forcing, via melting of submerged ice at the calving fronts of tidewater glaciers, has been identified as a possible driver of this behaviour. Such submarine melting may provide a significant direct contribution to the negative mass balance of the glacier and could also amplify calving rates. Quantification of submarine melting remains uncertain however since modelling of fjord circulation and submarine melting is challenging, hydrographic data from pro-glacial fjords are sparse and direct observation of submarine melting at a tidewater glacier has so far proved impossible. Here, we compare submarine melt rates obtained using buoyant plume theory to those from a numerical model (MITgcm), finding reasonable agreement between the two methods. We then use buoyant plume theory, due to its faster computational speed, to investigate the dependence of melt rate on subglacial discharge, subglacial channel size (and thus emerging flow velocity) and fjord-water temperature. Finally we apply the theory to real tidewater glaciers, finding significant gaps between modelled melt rates and those estimated from hydrographic data. We discuss possible reasons for such disagreements and their implications for constraining the importance of submarine melting to tidewater glacier mass balance.

  1. Characterization of Buoyant Fluorescent Particles for Field Observations of Water Flows

    PubMed Central

    Tauro, Flavia; Aureli, Matteo; Porfiri, Maurizio; Grimaldi, Salvatore

    2010-01-01

    In this paper, the feasibility of off-the-shelf buoyant fluorescent microspheres as particle tracers in turbid water flows is investigated. Microspheres’ fluorescence intensity is experimentally measured and detected in placid aqueous suspensions of increasing concentrations of clay to simulate typical conditions occurring in natural drainage networks. Experiments are conducted in a broad range of clay concentrations and particle immersion depths by using photoconductive cells and image-based sensing technologies. Results obtained with both methodologies exhibit comparable trends and show that the considered particles are fairly detectable in critically turbid water flows. Further information on performance and integration of the studied microspheres in low-cost measurement instrumentation for field observations is obtained through experiments conducted in a custom built miniature water channel. This experimental characterization provides a first assessment of the feasibility of commercially available buoyant fluorescent beads in the analysis of high turbidity surface water flows. The proposed technology may serve as a minimally invasive sensing system for hazardous events, such as pollutant diffusion in natural streams and flash flooding due to extreme rainfall. PMID:22163540

  2. Emission, Structure and Optical Properties of Overfire Soot from Buoyant Turbulent Diffusion Flames

    NASA Astrophysics Data System (ADS)

    Koylu, Umit Ozgur

    The present study investigated soot and carbon monoxide emissions, and evaluated the optical properties of soot, in the overfire region of buoyant turbulent diffusion flames burning in still air. Soot and carbon monoxide emissions, and the corresponding correlation between these emissions, were studied experimentally. The optical properties of soot were investigated both experimentally and theoretically. The experiments involved gas (acetylene, propylene, ethylene, propane, methane) and liquid (toluene, benzene, n-heptane, iso-propanol, ethanol, methanol) fuels. The investigation was limited to the fuel-lean (overfire) region of buoyant turbulent diffusion flames burning in still air. Measurements included flame heights, characteristic flame residence times, carbon monoxide and soot concentrations, mixture fractions, ex-situ soot structure parameters (primary particle sizes, number of primary particles in aggregates, fractal dimensions), and in-situ optical cross sections (differential scattering, total scattering, and absorption) of soot in the overfire region of buoyant turbulent diffusion flames, emphasizing conditions in the long residence time regime where these properties are independent of position in the overfire region and flame residence time. The predictions of optical cross sections for polydisperse aggregates were based on Rayleigh-Debye-Gans theory for fractal aggregates; the predictions of this theory were evaluated by combining the TEM structure and the light scattering/extinction measurements. Carbon monoxide concentrations and mixture fractions were correlated in the overfire region of gas- and liquid -fueled turbulent diffusion flames. Soot volume fraction state relationships were observed for liquid fuels, supporting earlier observations for gas fuels. A strong correlation between carbon monoxide and soot concentrations was established in the fuel-lean region of both gas- and liquid-fueled turbulent diffusion flames. The structure and emission

  3. Buoyant Response of the Tank 241-SY-101 Crust to Transfer and Back-Dilution

    SciTech Connect

    CW Stewart

    1999-11-08

    The mixer pump installed in Hanford Tank 241-SY-101 (SY-101) in July 1993 has prevented the large buoyant displacement gas release events (BD GRE) it has historically exhibited. But the absence of periodic disruption from GREs and the action of mixing have allowed the crust to grow. The accelerated gas retention has resulted in over 30 inches of waste level growth and the flammable gas volume stored in the crust has become a hazard. To remediate gas retention in the crust and the potential for buoyant displacement gas releases from below the crust, SY-101 will be diluted in the fall of 1999 to dissolve a large fraction of the solids in the tank. The plan is to transfer waste out and back-dilute with water in several steps of about 100,000 gallons each. Back-dilution water may be added at the transfer pump inlet, the base of the mixer pump, and on top of the crust. The mixer pump will continue to be required to prevent formation of a deep nonconnective layer and resumption of BD GREs. Therefore, it is vital to ensure that the transfer and back-dilution processes do not significantly degrade the pump's effectiveness. Part of the strategy to avoid mixer pump degradation is to keep the base of the crust layer well above the pump inlet, which is 236 inches above the tank bottom. The maximum transfer for which an equal back-dilution is possible without sinking the crust is 90 kgal if water is injected at the 96-inch transfer pump inlet and 120 kgal for injection at the 9-inch mixer pump burrowing ring. To keep the crust base above the lowest observed elevation of 295 inches, transfer and back-dilution must be limited to 143 kgal and 80 kgal, respectively, for the 96-inch back-dilution and 175 kgal with a 112 kgal back-dilution using the 9-inch back-dilution elevation. These limits can be avoided by adding water to the top of the crust to dissolve the negatively buoyant layers. If 20 kgal of water is placed on top of the crust and the rest of the back-dilution is placed

  4. Video Image Analysis of Turbulent Buoyant Jets Using a Novel Laboratory Apparatus

    NASA Astrophysics Data System (ADS)

    Crone, T. J.; Colgan, R. E.; Ferencevych, P. G.

    2012-12-01

    Turbulent buoyant jets play an important role in the transport of heat and mass in a variety of environmental settings on Earth. Naturally occurring examples include the discharges from high-temperature seafloor hydrothermal vents and from some types of subaerial volcanic eruptions. Anthropogenic examples include flows from industrial smokestacks and the flow from the damaged well after the Deepwater Horizon oil leak of 2010. Motivated by a desire to find non-invasive methods for measuring the volumetric flow rates of turbulent buoyant jets, we have constructed a laboratory apparatus that can generate these types of flows with easily adjustable nozzle velocities and fluid densities. The jet fluid comprises a variable mixture of nitrogen and carbon dioxide gas, which can be injected at any angle with respect to the vertical into the quiescent surrounding air. To make the flow visible we seed the jet fluid with a water fog generated by an array of piezoelectric diaphragms oscillating at ultrasonic frequencies. The system can generate jets that have initial densities ranging from approximately 2-48% greater than the ambient air. We obtain independent estimates of the volumetric flow rates using well-calibrated rotameters, and collect video image sequences for analysis at frame rates up to 120 frames per second using a machine vision camera. We are using this apparatus to investigate several outstanding problems related to the physics of these flows and their analysis using video imagery. First, we are working to better constrain several theoretical parameters that describe the trajectory of these flows when their initial velocities are not parallel to the buoyancy force. The ultimate goal of this effort is to develop well-calibrated methods for establishing volumetric flow rates using trajectory analysis. Second, we are working to refine optical plume velocimetry (OPV), a non-invasive technique for estimating flow rates using temporal cross-correlation of image

  5. Three-Dimensional Upward Flame Spreading in Partial-Gravity Buoyant Flows

    NASA Technical Reports Server (NTRS)

    Sacksteder, Kurt R.; Feier, Ioan I.; Shih, Hsin-Yi; T'ien, James S.

    2001-01-01

    Reduced-gravity environments have been used to establish low-speed, purely forced flows for both opposed- and concurrent-flow flame spread studies. Altenkirch's group obtained spacebased experimental results and developed unsteady, two-dimensional numerical simulations of opposed-flow flame spread including gas-phase radiation, primarily away from the flammability limit for thin fuels, but including observations of thick fuel quenching in quiescent environments. T'ien's group contributed some early flame spreading results for thin fuels both in opposed flow and concurrent flow regimes, with more focus on near-limit conditions. T'ien's group also developed two- and three-dimensional numerical simulations of concurrent-flow flame spread incorporating gas-phase radiative models, including predictions of a radiatively-induced quenching limit reached in very low-speed air flows. Radiative quenching has been subsequently observed in other studies of combustion in very low-speed flows including other flame spread investigations, droplet combustion and homogeneous diffusion flames, and is the subject of several contemporary studies reported in this workshop. Using NASA aircraft flying partial-gravity "parabolic" trajectories, flame spreading in purely buoyant, opposed-flow (downward burning) has been studied. These results indicated increases in flame spread rates and enhanced flammability (lower limiting atmospheric oxygen content) as gravity levels were reduced from normal Earth gravity, and were consistent with earlier data obtained by Altenkirch using a centrifuge. In this work, experimental results and a three-dimensional numerical simulation of upward flame spreading in variable partial-gravity environments were obtained including some effects of reduced pressure and variable sample width. The simulation provides physical insight for interpreting the experimental results and shows the intrinsic 3-D nature of buoyant, upward flame spreading. This study is intended to

  6. Under-Liquid Self-Assembly of Submerged Buoyant Polymer Particles.

    PubMed

    Multanen, Victor; Pogreb, Roman; Bormashenko, Yelena; Shulzinger, Evgeny; Whyman, Gene; Frenkel, Mark; Bormashenko, Edward

    2016-06-14

    The self-assembly of submerged cold-plasma-treated polyethylene beads (PBs) is reported. The plasma-treated immersed millimetrically sized PBs formed well-ordered 2D quasicrystalline structures. The submerged floating of "light" (buoyant) PBs is possible because of the energy gain achieved by the wetting of the high-energy plasma-treated polymer surface prevailing over the energy loss due to the upward climb of the liquid over the beads. The capillary "immersion" attraction force is responsible for the observed self-assembly. The observed 2D quasicrystalline structures demonstrate "dislocations" and "point defects". The mechanical vibration of self-assembled rafts built of PBs leads to the healing of point defects. The immersion capillary lateral force governs the self-assembly, whereas the elastic force is responsible for the repulsion of polymer beads. PMID:27193509

  7. Dynamics of single rising bubbles in neutrally buoyant liquid-solid suspensions.

    PubMed

    Hooshyar, Nasim; van Ommen, J Ruud; Hamersma, Peter J; Sundaresan, Sankaran; Mudde, Robert F

    2013-06-14

    We experimentally investigate the effect of particles on the dynamics of a gas bubble rising in a liquid-solid suspension while the particles are equally sized and neutrally buoyant. Using the Stokes number as a universal scale, we show that when a bubble rises through a suspension characterized by a low Stokes number (in our case, small particles), it will hardly collide with the particles and will experience the suspension as a pseudoclear liquid. On the other hand, when the Stokes number is high (large particles), the high particle inertia leads to direct collisions with the bubble. In that case, Newton's collision rule applies, and direct exchange of momentum and energy between the bubble and the particles occurs. We present a simple theory that describes the underlying mechanism determining the terminal bubble velocity. PMID:25165930

  8. Buoyant thermal plumes from planetary landers and rovers: Application to sizing of meteorological masts

    NASA Astrophysics Data System (ADS)

    Lorenz, Ralph D.; Sotzen, Kristin S.

    2014-01-01

    Objective. Landers on Mars and Titan may have warm surfaces as a result of solar heating or the carriage of radioisotope power sources. This warmth can perturb downwind meteorological measurements, but cannot be modeled as a simple aerodynamic wake because buoyant forces can be significant. Methods. We use an analytic model from the industrial aerodynamics literature on smoke dispersion from fires and smokestacks to evaluate the plume trajectories. Computational Fluid Dynamics (CFD) simulations are also performed for a Titan lander. Results. CFD yields results similar to the analytic model. (Albeit with a possibly weaker dependence on windspeed than the classic model.) We apply the models to evaluate the probability of immersion of instrumentation in plumes from the Mars Science Laboratory (MSL) Curiosity and for a Titan lander under various wind scenarios. Conclusions. Lander perturbations can be easily calculated. Practice implications. None.

  9. A numerical study of the motion of a neutrally buoyant cylinder in two dimensional shear flow

    NASA Astrophysics Data System (ADS)

    Pan, Tsorng-Whay; Huang, Shih-Lin; Chen, Shih-Di; Chu, Chin-Chou; Chang, Chien-Cheng

    2012-11-01

    We have investigated the motion of a neutrally buoyant cylinder of circular or elliptic shape in two dimensional shear flow of a Newtonian fluid by direct numerical simulation. The numerical results are validated by comparisons with existing theoretical, experimental and numerical results, including a power law of the normalized angular speed versus the particle Reynolds number. The centerline between two walls is an expected equilibrium position of the cylinder mass center in shear flow. When placing the particle away from the centerline initially, it migrates toward another equilibrium position for higher Reynolds numbers due to the interplay between the slip velocity, the Magnus force, and the wall repulsion force. T-W Pan acknowledges the support by the US NSF and S-L Huang, S-D Chen, C-C Chu, C-C Chang acknowledge the support by the National Science Council of Taiwan, ROC.

  10. Long-term tracking of neutrally buoyant tracer particles in two-dimensional fluid flows

    NASA Astrophysics Data System (ADS)

    Pervez, M. S.; Solomon, T. H.

    1994-07-01

    An experimental technique has been developed to produce and to track neutrally buoyant particles in a two-dimensional fluid flow. The key aspect of the technique is the ability to track particles for extended intervals (over an hour), which is essential for quantitative studies of transport and mixing. The approach is composed of two stages. In the first stage, digital image processing hardware partially processes the images, reducing the data rate to 50 kbyte/s (typically) and allowing several hours of data to be stored on a conventional computer disk. In the second stage, programs extract particle trajectories from the reduced data. The approach is tested in an experiment on planetary-type flows in a rotating annulus. In an appendix, a technique is discussed for fabricating wax or crayon particles with arbitrary density.

  11. Experimental insights on the development of buoyant plumes injected into a porous media

    NASA Astrophysics Data System (ADS)

    Lyu, Xiaoying; Woods, Andrew W.

    2016-01-01

    We describe a series of new laboratory experiments which examine the rise of a two-dimensional buoyancy-driven plume of freshwater through a porous layer initially saturated with aqueous saline solution. Measurements show that the plume head accounts for a constant fraction of about 0.7 of the buoyancy supplied at the source and that it grows as it rises through the porous layer. However, the morphology of the plume head becomes increasingly complex as the ratio of the injection speed to the buoyancy rise speed increases, with the fluid spreading laterally and developing localized buoyant fingers which intermingle with the ambient fluid. Behind the plume head, a tail of nearly constant width develops providing a pathway from the source to the plume head. These starting plume dynamics may be relevant for buoyancy-driven contaminant dispersal and also for the convection which develops during CO2 sequestration as CO2 dissolves into aquifer water.

  12. Translational and rotational dynamics of a large buoyant sphere in turbulence

    NASA Astrophysics Data System (ADS)

    Mathai, Varghese; Neut, Matthijs W. M.; van der Poel, Erwin P.; Sun, Chao

    2016-04-01

    We report experimental measurements of the translational and rotational dynamics of a large buoyant sphere in isotropic turbulence. We introduce an efficient method to simultaneously determine the position and (absolute) orientation of a spherical body from visual observation. The method employs a minimization algorithm to obtain the orientation from the 2D projection of a specific pattern drawn onto the surface of the sphere. This has the advantages that it does not require a database of reference images, is easily scalable using parallel processing, and enables accurate absolute orientation reference. Analysis of the sphere's translational dynamics reveals clear differences between the streamwise and transverse directions. The translational autocorrelations and PDFs provide evidence for periodicity in the particle's dynamics even under turbulent conditions. The angular autocorrelations show weak periodicity. The angular accelerations exhibit wide tails, however without a directional dependence.

  13. Buoyant Effects on the Flammability of Silicone Samples Planned for the Spacecraft Fire Experiment (Saffire)

    NASA Technical Reports Server (NTRS)

    Niehaus, Justin E.; Ferkul, Paul V.; Gokoglu, Suleyman A.; Ruff, Gary A.

    2015-01-01

    Flammability experiments on silicone samples were conducted in anticipation of the Spacecraft Fire Experiment (Saffire). The sample geometry was chosen to match the NASA 6001 Test 1 specification, namely 5 cm wide by 30 cm tall. Four thicknesses of silicone (0.25, 0.36, 0.61 and 1.00 mm) were examined. Tests included traditional upward buoyant flame spread using Test 1 procedures, downward opposed-flow flame spread, horizontal and angled flame spread, and forced-flow upward and downward flame spread. In addition to these configurations, upward and downward tests were conducted in a chamber with varying oxygen concentrations. In the upward buoyant flame spread tests, the flame generally did not burn the entire sample. As thickness was increased, the flame spread distance decreased before flame extinguishment. For the thickest sample, ignition could not be achieved. In the downward tests, the two thinnest samples permitted the flame to burn the entire sample, but the spread rate was lower compared to the corresponding upward values. The other two thicknesses could not be ignited in the downward configuration. The increased flammability for downward spreading flames relative to upward ones is uncommon. The two thinnest samples also burned completely in the horizontal configuration, as well as at angles up to 75 degrees from the horizontal. Upward tests in air with an added forced flow were more flammable. The upward and downward flammability behavior was compared in atmospheres of varying oxygen concentration to determine a maximum oxygen concentration for each configuration. Complementary analyses using EDS, TGA, and SEM techniques suggest the importance of the silica layer deposited downstream onto the unburned sample surface.

  14. The spatial distribution and speciation of iron in buoyant hydrothermal plumes of the Mid-Cayman Rise

    NASA Astrophysics Data System (ADS)

    Cron, B. R.; Toner, B. M.; Bennett, S. A.; German, C. R.; Dick, G.; Breier, J. A.

    2012-12-01

    Biogeochemical cycling of elements, such as iron and sulfur, at mid-ocean ridge spreading centers may modulate hydrothermal fluxes to the ocean. To better understand the nature and scale of these processes, the geochemical gradients in buoyant plumes were examined at the Mid-Cayman Rise, a short (~110 km) ultra-slow spreading center in the Caribbean Sea that hosts the deepest known high temperature venting. Changes in particulate iron and sulfur speciation were measured in the first 40-50 m of buoyant plumes at two vent fields, Von Damm (2,300m) and Piccard (5,000m). These data will be used to identify products of precipitation reactions and define particulate energy sources available for microbial metabolism. A series of samples were collected by in situ filtration at 0.5 m and 50 m above the Beebe Vents, Piccard hydrothermal field and at 1 m, 8 m, and 40 m above the central spire of the Von Damm vent field using the ROV Jason and CTD-casts. Samples were packaged under dinitrogen and frozen shipboard to preserve oxidation-reduction sensitive species for microprobe Fe 1s and S 1s X-ray absorption near edge structure (XANES) spectroscopy (Advanced Light Source, Lawrence Berkeley National Laboratory, beamline 10.3.2). The Von Damm vent is characterized by shimmering vent fluids with dilute particulates in the buoyant plume. Within the particulate phase, the Von Damm buoyant plume was comprised of 38 mol % Fe-sulfides, 40 mol % Fe(II), and 21 mol % Fe(III) at 1 m. At 8 m it is comprised of 32 mol % Fe-sulfides, 7 % Fe(II), and 59 mol % Fe(III). When the plume reaches 40 m, it is 6 mol % Fe-sulfides, 8 mol % Fe(II), 72 mol % Fe(III), and 14 mol % Fe(0). The Beebe vents are characterized by very dense particle formation in their buoyant plumes. The Beebe vent plume sampled comprised 65 mol % sulfides, 3 % mol Fe(II) & 32 mol % Fe(III)¬¬¬¬ at 0.5 m. As the plume reached 50 m above the vent, the fluids were 43 mol % sulfide and 56 mol % Fe(III). Both buoyant plume

  15. 2D and 3D numerical models on compositionally buoyant diapirs in the mantle wedge

    NASA Astrophysics Data System (ADS)

    Hasenclever, Jörg; Morgan, Jason Phipps; Hort, Matthias; Rüpke, Lars H.

    2011-11-01

    We present 2D and 3D numerical model calculations that focus on the physics of compositionally buoyant diapirs rising within a mantle wedge corner flow. Compositional buoyancy is assumed to arise from slab dehydration during which water-rich volatiles enter the mantle wedge and form a wet, less dense boundary layer on top of the slab. Slab dehydration is prescribed to occur in the 80-180 km deep slab interval, and the water transport is treated as a diffusion-like process. In this study, the mantle's rheology is modeled as being isoviscous for the benefit of easier-to-interpret feedbacks between water migration and buoyant viscous flow of the mantle. We use a simple subduction geometry that does not change during the numerical calculation. In a large set of 2D calculations we have identified that five different flow regimes can form, in which the position, number, and formation time of the diapirs vary as a function of four parameters: subduction angle, subduction rate, water diffusivity (mobility), and mantle viscosity. Using the same numerical method and numerical resolution we also conducted a suite of 3D calculations for 16 selected parameter combinations. Comparing the 2D and 3D results for the same model parameters reveals that the 2D models can only give limited insights into the inherently 3D problem of mantle wedge diapirism. While often correctly predicting the position and onset time of the first diapir(s), the 2D models fail to capture the dynamics of diapir ascent as well as the formation of secondary diapirs that result from boundary layer perturbations caused by previous diapirs. Of greatest importance for physically correct results is the numerical resolution in the region where diapirs nucleate, which must be high enough to accurately capture the growth of the thin wet boundary layer on top of the slab and, subsequently, the formation, morphology, and ascent of diapirs. Here 2D models can be very useful to quantify the required resolution, which we

  16. The Melt Segregation During Ascent of Buoyant Diapirs in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Zhang, N.; Behn, M. D.; Parmentier, E. M.; Kincaid, C. R.

    2014-12-01

    Cold, low-density diapirs arising from hydrated mantle and/or subducted sediments on the top of subducting slabs may transport key chemical signatures from the slab to the shallow source region for arc magmas. These chemical signatures are strongly influenced by melting of this buoyant material during its ascent. However, to date there have been relatively few quantitative models to constrain melting and melt segregation in an ascending diapir, as well as the induced geochemical signature. Here, we use a two-phase Darcy-Stokes-energy model to investigate thermal evolution, melting, and melt segregation in buoyant diapirs as they ascend through the mantle wedge. Using a simplified 2-D axi-symmetric circular geometry we investigate diapir evolution in three scenarios with increasing complexity. First, we consider a case without melting in which the thermal evolution of the diapir is controlled solely by thermal diffusion during ascent. Our results show that for most cases (e.g., diapir radius ≤ 3.7 km and diapir generation depths of ~ 75 km) thermal diffusion times are smaller than the ascent time—implying that the diapir will thermal equilibrate with the mantle wedge. Secondly, we parameterize melting within the diapir, but without melt segregation, and add the effect of latent heat to the thermal evolution of the diapir. Latent heat significantly buffers heating of the diapir. For the diapir with radius ~3.7 km, the heating from the outside is slowed down ~30%. Finally, we include melt segregation within the diapir in the model. Melting initiates at the boundaries of the diapir as the cold interior warms in response to thermal equilibration with the hot mantle wedge. This forms a high porosity, high permeability rim around the margin of the diapir. As the diapir continues to warm and ascend, new melts migrate into this rim and are focused upward, accumulating at the top of the diapir. The rim thus acts like an annulus melt channel isolating the central part of

  17. Evolution of localized blobs of swirling or buoyant fluid with and without an ambient magnetic field

    SciTech Connect

    Davidson, P. A.; Sreenivasan, Binod; Aspden, A. J.

    2007-02-15

    We investigate the evolution of localized blobs of swirling or buoyant fluid in an infinite, inviscid, electrically conducting fluid. We consider the three cases of a strong imposed magnetic field, a weak imposed magnetic field, and no magnetic field. For a swirling blob in the absence of a magnetic field, we find, in line with others, that the blob bursts radially outward under the action of the centrifugal force, forming a thin annular vortex sheet. A simple model of this process predicts that the vortex sheet thins exponentially fast and that it moves radially outward with constant velocity. These predictions are verified by high-resolution numerical simulations. When an intense magnetic field is applied, this phenomenon is suppressed, with the energy and angular momentum of the blob now diffusing axially along the magnetic field lines, converting the blob into a columnar structure. For modest or weak magnetic fields, there are elements of both types of behavior, with the radial bursting dominating over axial diffusion for weak fields. However, even when the magnetic field is very weak, the flow structure is quite distinct to that of the nonmagnetic case. In particular, a small but finite magnetic field places a lower bound on the thickness of the annular vortex sheet and produces an annulus of counter-rotating fluid that surrounds the vortex core. The behavior of the buoyant blob is similar. In the absence of a magnetic field, it rapidly develops the mushroomlike shape of a thermal, with a thin vortex sheet at the top and sides of the mushroom. Again, a simple model of this process predicts that the vortex sheet at the top of the thermal thins exponentially fast and rises with constant velocity. These predictions are consistent with earlier numerical simulations. Curiously, however, it is shown that the net vertical momentum associated with the blob increases linearly in time, despite the fact that the vertical velocity at the front of the thermal is constant

  18. Dispersal of volcaniclasts during deep-sea eruptions: Settling velocities and entrainment in buoyant seawater plumes

    NASA Astrophysics Data System (ADS)

    Barreyre, Thibaut; Soule, S. Adam; Sohn, Robert A.

    2011-08-01

    We use tank experiments to measure settling rates of deep-sea volcaniclastic material recovered from the Arctic (85°E Gakkel Ridge) and Pacific (Juan de Fuca Ridge, Loihi seamount) Oceans. We find that clast size and shape exert a strong influence on settling velocity, with velocities of ~ 30 cm/s for large (~ 8 mm), blocky clasts, compared to velocities of ~ 2.5 cm/s for small (< 0.5 mm), sheet-like clasts. We fit our observations to the generalized model of Ferguson and Church (2004) to establish empirical scaling laws for settling velocity, and then use these results to test the hypothesis that entrainment in a buoyant plume of hot seawater is an important dispersal mechanism for volcaniclastic material in the deep-sea (Clague et al., 2009). We superpose the observed settling rates on velocity fields generated with the Morton et al. (1956) model for turbulent plumes in stratified media to estimate the rise height of the clastic material under water column conditions corresponding to the Gakkel and Juan de Fuca (JdFR) Ridges, and then estimate dispersal distances assuming the grains settle to the seafloor while being advected in lateral currents. Dispersal distances in our model are a function plume strength (i.e., buoyancy flux), lateral current speeds, and clast settling velocity. Our model demonstrates that large (30 GW) eruption 'megaplumes' can loft volcaniclastic material more than a kilometer above the seafloor where entrainment in deep-sea currents can advect dominant clast types (~ 1 mm, blocky grains) up to a few hundred meters from a source vent. Small bubble-wall fragments (e.g., limu o Pele) entrained in a megaplume could be advected as far as a few kilometers from a source region. These results indicate that entrainment in buoyant seawater plumes during an eruption may play an important role in clast dispersal, but it is not clear if this mechanism can explain the distribution of volcaniclastic material at the sites on the Gakkel and Juan de Fuca

  19. Buoyant Effects on the Flammability of Silicone Samples Planned for the Spacecraft Fire Experiment (Saffire)

    NASA Technical Reports Server (NTRS)

    Niehaus, Justin; Ferkul, Paul V.; Gokoglu, Suleyman; Ruff, Gary

    2015-01-01

    Flammability experiments on silicone samples were conducted in anticipation of the Spacecraft Fire Experiment (Saffire). The sample geometry was chosen to match the NASA 6001 Test 1 specification, namely 5 cm wide by 30 cm tall. Four thicknesses of silicone (0.25, 0.36, 0.61 and 1.00 mm) were examined. Tests included traditional upward buoyant flame spread using Test 1 procedures, downward opposed flow flame spread, horizontal and angled flame spread, forced flow upward and downward flame spread. In addition to these configurations, upward and downward tests were also conducted in a chamber with varying oxygen concentrations. In the upward buoyant flame spread tests, the flame generally did not burn the entire sample. As thickness was increased, the flame spread distance decreased before flame extinguishment. For the thickest sample, ignition could not be achieved. In the downward tests, the two thinnest samples permitted the flame to burn the entire sample, but the spread rate was lower compared to the corresponding upward values. The other two thicknesses could not be ignited in the downward configuration. The increased flammability for downward spreading flames relative to upward ones is uncommon. The two thinnest samples also burned completely in the horizontal configuration, as well as at angles up to 75 degrees from the horizontal. The upward and downward flammability behavior was compared in atmospheres of varying oxygen concentration to determine a maximum oxygen concentration for each configuration. Upward tests in air with an added forced flow were more flammable. Complementary analyses using SEM and TGA techniques suggest the importance of the silica layer formed on the burned sample surface. As silicone burns upward, silica deposits downstream •If the silicone is ignited in the downward configuration, it burns the entire length of the sample •Burning upward at an angle increases the burn length in some cases possibly due to less silica deposition

  20. An EOF analysis of HF Doppler radar current measurements of the Chesapeake Bay buoyant outflow

    NASA Astrophysics Data System (ADS)

    Marmorino, G. O.; Shay, L. K.; Haus, B. K.; Handler, R. A.; Graber, H. C.; Horne, M. P.

    1999-02-01

    Surface currents measured by HF Doppler radar as part of a study of the Chesapeake Bay outflow plume are examined using a 'real-vector' empirical orthogonal function (EOF) analysis (Kaihatu et al., 1998). Based on about 23 days of nearly continuous data, the analysis shows that the first three EOF modes, judged to be the only significant modes, account for 76% of the variance in the data set. The buoyant outflow occurs primarily in the mean flow field. The first EOF mode is dominated by wind forcing and the second mode by across-shelf semi-diurnal tidal forcing. The third mode exhibits a large-scale horizontal shear and contains a curved region of weak relative flow which appears to delineate the offshore edge of the plume; also, the third-mode response varies over the spring-neap cycle, suggesting a modulation of the outflow plume by a tidal residual eddy. The analysis therefore has provided a useful, exploratory examination of this dataset of surface currents.

  1. FPluMe: An integral eruption column model based on the Buoyant Plume Theory

    NASA Astrophysics Data System (ADS)

    Folch, Arnau; Costa, Antonio; Macedonio, Giovanni

    2015-04-01

    Estimates of mass flow rate from volcanic eruption columns are crucial for ash dispersion models, used to assess hazard on population and civil aviation. We present a practical model of eruption column model based on the Buoyant Plume Theory (BPT) that accounts for the effect of the atmospheric wind that results in the bending over of the plume trajectory and increases the entrainment of ambient air. The model solves the equations for the conservation of mass, momentum and energy in terms of averaged variables, accounting for fallout and re-entrainment of tephra from and into the column and particle aggregation. For some given atmospheric conditions and a wind profile, the model can be used to determine the height at which volcanic plumes spread in the atmosphere if mass flow rate at the vent is known, or to estimate mass flow rate when the eruption column height is known. For a given column height, if wind effects are not properly accounted for, the values of the mass flow rate can be significantly underestimated. Our model calculations are compared with proposed semi-empirical relationships between the plume height and the source mass flux that account for the atmospheric wind effect.

  2. Reexamination of the Association Between Melting Point, Buoyant Density, and Chemical Base Composition of Deoxyribonucleic Acid

    PubMed Central

    De Ley, J.

    1970-01-01

    The equations currently used for the calculation of the chemical base composition of deoxyribonucleic acid (DNA), expressed as moles per cent guanine plus cytosine (% GC), from either buoyant density (ρ) or midpoint of thermal denaturation (Tm) were recalculated by using only sets of data on DNA determined with the same strains. All available information from the literature was screened and supplemented by unpublished data. The results were calculated by regression and correlation analysis and treated statistically. From the data on 96 strains of bacteria, it was calculated that% GC = 2.44 (Tm – 69.4). Tm appears to be unaffected by the substitution of cytosine by hydroxymethylcytosine. This equation is also valid for nonbacterial DNA. From the data on 84 strains of bacteria, the relation% GC = 1038.47 (–1.6616) was calculated. The constants in this equation are slightly modified when data on nonbacterial DNA are included. Both correlations differ only slightly from those currently used, but now they lean on a statistically sound basis. As a control, the relation between ρ and Tm was calculated from data of 197 strains; it agrees excellently with the above two equations. PMID:5438045

  3. Generation of a buoyant jet by a sphere moving vertically in a stratified fluid

    NASA Astrophysics Data System (ADS)

    Hanazaki, Hideshi; Shimobata, Keisuke; Yoshikawa, Hiroyasu

    2011-11-01

    We consider the flow past a sphere moving vertically at a constant speed in salt-stratified fluid. Experiments have shown that vertical jets are generated even if the vertical mean density gradient is not large. At least seven types of wake structures have been found, including a thin jet with a surrounding bell-shaped structure. In this numerical study, we investigate the unsteady generation mechanism of buoyant jets with the focus on the diffusion effects of the density/salt. When a sphere descends in a stratified fluid, the density is initially conserved along the movement of the fluid and the originally horizontal isopycnal surfaces are simply deformed vertically and pulled down by the sphere. As time proceeds, diffusive effects become significant in the density boudary layer on the sphere surface and in the thin jet, and the density is no longer conserved. This violation of conservation would be the origin of the jet which is composed of the fluids which moves up to return to thier original heights.

  4. Magnetic Cycles and Buoyant Magnetic Structures in a Rapidly Rotating Sun

    NASA Astrophysics Data System (ADS)

    Nelson, Nicholas J.; Brown, B. P.; Brun, S.; Miesch, M. S.; Toomre, J.

    2011-01-01

    Observations of sun-like stars rotating faster than our current sun show that they exhibit solar-like magnetic cycles and features, such as star spots. Using global 3-D simulations to study the coupling of large-scale convection, rotation, and magnetism in a younger sun, we have probed the effects of more rapid rotation on stellar dynamos and the nature of magnetic cycles. Our anelastic spherical harmonics (ASH) code allows study of the convective envelope, occupying the outer 30% by radius of a sun-like star. Major MHD simulations carried out at three times the current solar rotation rate reveal magnetic dynamo action that can produce wreaths of strong toroidal magnetic field at low latitudes, often with opposite polarity in the two hemispheres. The presence of the wreaths is quite surprising, for they arise as quite persistent global structures amidst the vigorous and turbulent convection. We have recently explored behavior in systems with considerably lower diffusivities, achieved with a dynamic Smagorinsky treatment of unresolved turbulence. The lower levels of diffusion create magnetic wreaths that undergo prominent variations in field strength, even exhibiting global magnetic cycles that involve polarity reversals. Additionally, during the cycle maximum, when magnetic energies and mean magnetic fields peak, the wreaths possess buoyant magnetic structures that rise coherently through much of the convective envelope via a combination of advection by convective upflows and magnetic buoyancy. We explore aspects of these rising magnetic structures and the evolving global dynamo action which produces them.

  5. Poiseuille flow of a mixture of neutrally buoyant particles in a fluid

    SciTech Connect

    Reinerrsman, P.N.

    1988-01-01

    Constitutive equations are given for the stress, couple stress, and interphase momentum transfer in a mixture consisting of neutrally buoyant particles in a fluid. The interphase momentum transfer terms include objective expressions quantifying Stokes; drag, Faxen force, shear life, Magnus lift, and rotational drag. Coefficients of the drag and lift terms are deduced from macroscopic theory. The viscosity of the solid phase and the cross viscosities are estimated to coincide with previous work in micropolar flow theory. The resulting equations of motion are solved numerically for this general model and for the subset of this model which complies with the principle of phase separation. These solutions are compared with the flows predicted by micropolar theory. Although the micropolar theory may provide a good approximation for multiphase flow in some regimes, micropolar theory cannot model the phase velocity differences and volume fraction gradients that occur in high pressure, small channel flow. The effect of controlling the boundary values of particle and fluid spin is investigated, including the effect of back spin and symmetric spin.

  6. Numerical simulation of 2D buoyant jets in ice-covered and temperature-stratified water

    NASA Astrophysics Data System (ADS)

    Gu, Ruochuan

    A two-dimensional (2D) unsteady simulation model is applied to the problem of a submerged warm water discharge into a stratified lake or reservoir with an ice cover. Numerical simulations and analyses are conducted to gain insight into large-scale convective recirculation and flow processes in a cold waterbody induced by a buoyant jet. Jet behaviors under various discharge temperatures are captured by directly modeling flow and thermal fields. Flow structures and processes are described by the simulated spatial and temporal distributions of velocity and temperature in various regions: deflection, recirculation, attachment, and impingement. Some peculiar hydrothermal and dynamic features, e.g. reversal of buoyancy due to the dilution of a warm jet by entraining cold ambient water, are identified and examined. Simulation results show that buoyancy is the most important factor controlling jet behavior and mixing processes. The inflow boundary is treated as a liquid wall from which the jet is offset. Similarity and difference in effects of boundaries perpendicular and parallel to flow, and of buoyancy on jet attachment and impingement, are discussed. Symmetric flow configuration is used to de-emphasize the Coanda effect caused by offset.

  7. Buoyant instabilities in downward flow in a symmetrically heated vertical channel

    SciTech Connect

    Evans, G.; Greif, R.

    1996-07-01

    This study of the downward flow of nitrogen in a tall, partially heated vertical channel (upstream isothermal at T{sub in}*, heated region isothermal at T{sub s}* downstream adiabatic) shows the strong effects of buoyancy even for small temperature differences. Time-dependent oscillations including periodic flow reversals occur along the channel walls. Although the flow and heat transfer are asymmetric, the temperature and axial component of velocity show symmetric reflections at two times that are half a period apart and the lateral component of velocity shows antisymmetric reflections at the two times. There is strong interaction between the downward flow in the central region of the channel and the upward flow along the heated channel walls. At the top of the heated region, the upward buoyant flow turns toward the center of the channel and is incorporated into the downward flow. Along the channel centerline there are nonmonotonic variations of the axial component of velocity and temperature and a large lateral component of velocity that reverses direction periodically. Results are presented for Re = 219.7 and Gr/Re{sup 2} = 1.83, 8.0, and 13.7. The heat transfer and the frequency of the oscillations increases and the flow and temperature fields become more complex as Gr/Re{sup 2} increases. The results have applications to fiber drying, food processing, crystal growth, solar energy collection, cooling of electronic circuits, ventilation, etc.

  8. 3D Mixing Inside a Neutrally Buoyant Drop Driven by Electrohydrodynamic Flows

    NASA Astrophysics Data System (ADS)

    Xu, Xiumei; Homsy, G. M.

    2007-11-01

    For a neutrally buoyant drop subjected to a uniform electric field, the internal flow is the well-known Taylor circulation. In Phys. Fluids 19 013102 (2007), we theoretically studied three dimensional mixing by periodically switching a uniform electric field through an angle α. Periodically switching the field is equivalent to periodically changing the symmetry axis of the Taylor circulation. For α=0.5 π, there is no chaotic mixing because the common heteroclinic trajectories form the separatrix of the flow. For other switching angles, chaotic advection is generated due to perturbations of the heteroclinic trajectory. Experimental investigations of mixing were carried out using a nearly isopycnic silicone oil/castor oil system. For α=0.5 π, our experiments show the existence of symmetry planes. In addition, two blobs of particles are observed to maintain almost invariant shapes for very long time, indicating the absence of chaotic mixing, as predicted by the theory. For other switching angles, experiments show the penetration of symmetry planes by tracer particles. However it is difficult to draw definitive conclusions regarding chaotic mixing because of charge relaxation, long initial transients and drop translation effects.

  9. Wave induced mixing and transport of buoyant particles: application to the Statfjord A oil spill

    NASA Astrophysics Data System (ADS)

    Drivdal, M.; Broström, G.; Christensen, K. H.

    2014-05-01

    The modelling of wave-current and wave-turbulence interactions have received much attention in recent years. In this study the focus is on how these wave effects modify the transport of particles in the ocean. Here the particles are buoyant tracers that can represent oil droplets, plastic particles or plankton, for example fish eggs and larvae. Using the General Ocean Turbulence Model (GOTM), modified to take surface wave effects into account, we investigate how the increased mixing by wave breaking and Stokes shear production as well as the stronger veering by the Coriolis-Stokes force affect the drift of the particles. The energy and momentum fluxes as well as the Stokes drift depend on the directional wave spectrum that can be obtained from a wave model or from observations. As a first test the depth and velocity scales from the model are compared with analytical solutions based on a constant eddy viscosity (e.g. classical Ekman theory). Secondly the model is applied to a case where we investigate the oil drift after an offshore oil spill outside the western coast of Norway in 2007. During this accident the average net drift of oil was observed to be both slower and more deflected away from the wind direction than predicted by empirical models. With wind and wave forcing from the ERA Interim archive, it is shown that the wave effects are important for the resultant drift in this case, and has the potential to improve drift forecasting.

  10. Wave-induced mixing and transport of buoyant particles: application to the Statfjord A oil spill

    NASA Astrophysics Data System (ADS)

    Drivdal, M.; Broström, G.; Christensen, K. H.

    2014-12-01

    This study focuses on how wave-current and wave-turbulence interactions modify the transport of buoyant particles in the ocean. Here the particles can represent oil droplets, plastic particles, or plankton such as fish eggs and larvae. Using the General Ocean Turbulence Model (GOTM), modified to take surface wave effects into account, we investigate how the increased mixing by wave breaking and Stokes shear production, as well as the stronger veering by the Coriolis-Stokes force, affects the drift of the particles. The energy and momentum fluxes, as well as the Stokes drift, depend on the directional wave spectrum obtained from a wave model. As a first test, the depth and velocity scales from the model are compared with analytical solutions based on a constant eddy viscosity (i.e., classical Ekman theory). Secondly, the model is applied to a case in which we investigate the oil drift after an oil spill off the west coast of Norway in 2007. During this accident the average net drift of oil was observed to be both slower and more deflected away from the wind direction than predicted by oil-drift models. In this case, using wind and wave forcing from the ERA Interim archive it is shown that the wave effects are important for the resultant drift and have the potential to improve drift forecasting.

  11. Near Surface Vapor Bubble Layers in Buoyant Low Stretch Burning of Polymethylmethacrylate

    NASA Technical Reports Server (NTRS)

    Olson, Sandra L.; Tien, J. S.

    1999-01-01

    Large-scale buoyant low stretch stagnation point diffusion flames over solid fuel (polymethylmethacrylate) were studied for a range of aerodynamic stretch rates of 2-12/ sec which are of the same order as spacecraft ventilation-induced stretch in a microgravity environment. An extensive layer of polymer material above the glass transition temperature is observed. Unique phenomena associated with this extensive glass layer included substantial swelling of the burning surface, in-depth bubble formation, and migration and/or elongation of the bubbles normal to the hot surface. The bubble layer acted to insulate the polymer surface by reducing the effective conductivity of the solid. The reduced in-depth conduction stabilized the flame for longer than expected from theory neglecting the bubble layer. While buoyancy acts to move the bubbles deeper into the molten polymer, thermocapillary forces and surface regression both act to bring the bubbles to the burning surface. Bubble layers may thus be very important in low gravity (low stretch) burning of materials. As bubbles reached the burning surface, monomer fuel vapors jetted from the surface, enhancing burning by entraining ambient air flow. Popping of these bubbles at the surface can expel burning droplets of the molten material, which may increase the fire propagation hazards at low stretch rates.

  12. Turbulent channel flow laden with finite-size neutrally-buoyant particles

    NASA Astrophysics Data System (ADS)

    Picano, Francesco; Breugem, Wim-Paul; Brandt, Luca

    2014-11-01

    Dense suspensions are widely encountered in many applications and in environmental flows. While their rheological features in laminar flows have been longly studied, much less is known on their behavior in turbulent/inertial regime. The present works aims to fill this gap by investigating the turbulent channel flow of a Newtonian fluid laden with rigid neutrally-buoyant spheres at relatively high volume fractions. An Immersed Boundary Method has been used to account for the phase interaction performing Direct Numerical Simulation in the range of volume fractions Φ = 0 - 0 . 2 and a typical particle radius of 10 wall units. The results show that the mean velocity profiles are significantly altered by the presence of a solid phase with a decrease of the von Karman constant in the log-law. The overall drag is found to monotonically increase with the volume fraction. At the highest volume fraction here investigated, Φ = 0 . 2 , the velocity fluctuation intensities and the Reynolds shear stress are found to decrease. The analysis of the mean momentum balance shows that the particle-induced stresses govern the dynamics in the dense cases and are responsible of the the overall drag increase since the turbulent shear stress is reduced with respect the unladen case. This work was supported by the European Research Council Grant No. ERC-2013-CoG-616186, TRITOS.

  13. Turbulence Modeling Effects on the Prediction of Equilibrium States of Buoyant Shear Flows

    NASA Technical Reports Server (NTRS)

    Zhao, C. Y.; So, R. M. C.; Gatski, T. B.

    2001-01-01

    The effects of turbulence modeling on the prediction of equilibrium states of turbulent buoyant shear flows were investigated. The velocity field models used include a two-equation closure, a Reynolds-stress closure assuming two different pressure-strain models and three different dissipation rate tensor models. As for the thermal field closure models, two different pressure-scrambling models and nine different temperature variance dissipation rate, Epsilon(0) equations were considered. The emphasis of this paper is focused on the effects of the Epsilon(0)-equation, of the dissipation rate models, of the pressure-strain models and of the pressure-scrambling models on the prediction of the approach to equilibrium turbulence. Equilibrium turbulence is defined by the time rate (if change of the scaled Reynolds stress anisotropic tensor and heat flux vector becoming zero. These conditions lead to the equilibrium state parameters. Calculations show that the Epsilon(0)-equation has a significant effect on the prediction of the approach to equilibrium turbulence. For a particular Epsilon(0)-equation, all velocity closure models considered give an equilibrium state if anisotropic dissipation is accounted for in one form or another in the dissipation rate tensor or in the Epsilon(0)-equation. It is further found that the models considered for the pressure-strain tensor and the pressure-scrambling vector have little or no effect on the prediction of the approach to equilibrium turbulence.

  14. Laser soot-scattering imaging of a large buoyant diffusion flame

    SciTech Connect

    Lye, R.C.M.; Toner, S.J.

    1987-01-01

    A novel diagnostic technique, which makes use of laser light scattered by soot particles, was used in an effort to identify the flame sheets within a natural gas diffusion flame. Soot particles, inherently created and consumed in the flame, were used as the scattering medium, which obviated the need for externally supplied seed material. Since no foreign material was added to the flame, the current technique can be considered truly nonintrusive. The soot distribution within a large buoyant natural gas diffusion flame is argued to be a reasonable marker of the flame sheets. Measurements made in 47.4-190 kW natural gas flames stabilized on a 0.5 m diameter burner show that the flame sheets are highly wrinkled and convoluted surfaces. The flame sheets are distributed fairly uniformly within the instantaneous volume of the flame, based on images of the associated soot, and the instantaneous flame volume is devoid of soot for 40-60% of the time. When soot is present, it is observed as thin sheets which become narrower in regions where the average strain rate is estimated to be greater.

  15. 46 CFR 160.060-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... closure for buoyant vests must— (1) Be tested for weathering. The Coast Guard will determine which one or...) for 24 hours; and (2) Within 5 minutes of completion of the weathering test required by paragraph...

  16. The effect of viscosity variation on the stability of a buoyantly unstable miscible layer in vertical porous media

    NASA Astrophysics Data System (ADS)

    Pramanik, Satyajit; Hota, Tapan Kumar; Mishra, Manoranjan

    We numerically show that in the absence of displacement a buoyantly unstable miscible layer with variable viscosity is less unstable than the constant viscosity layers. With the help of scaling analysis, we proved that the dynamics of variable viscosity layers with stable as well as unstable viscosity contrasts are identical in the absence of displacement. When the heavier fluid displaces the lighter one, the influence of viscosity contrast on the buoyantly unstable miscible layer is analogous to that in neutrally buoyant fluids. These findings of direct numerical simulations (DNS) in the fully nonlinear regime are consistent with the linear stability analysis (LSA). Furthermore, we perform a non-modal stability analysis of the linearized equations, which depicts the qualitative agreement with both LSA and DNS. In addition, the response of the linearized operator to external excitation has been studied through pseudospectra. The present findings are of great importance to understand the hydrodynamic mechanisms involved in geologic carbon sequestration. SP gratefully acknowledges the financial support from the National Board for Higher Mathematics through a Ph.D. fellowship.

  17. Genetic affinities between trans-oceanic populations of non-buoyant macroalgae in the high latitudes of the Southern Hemisphere.

    PubMed

    Fraser, Ceridwen I; Zuccarello, Giuseppe C; Spencer, Hamish G; Salvatore, Laura C; Garcia, Gabriella R; Waters, Jonathan M

    2013-01-01

    Marine biologists and biogeographers have long been puzzled by apparently non-dispersive coastal taxa that nonetheless have extensive transoceanic distributions. We here carried out a broad-scale phylogeographic study to test whether two widespread Southern Hemisphere species of non-buoyant littoral macroalgae are capable of long-distance dispersal. Samples were collected from along the coasts of southern Chile, New Zealand and several subAntarctic islands, with the focus on high latitude populations in the path of the Antarctic Circumpolar Current or West Wind Drift. We targeted two widespread littoral macroalgal species: the brown alga Adenocystisutricularis (Ectocarpales, Heterokontophyta) and the red alga Bostrychiaintricata (Ceramiales, Rhodophyta). Phylogenetic analyses were performed using partial mitochondrial (COI), chloroplast (rbcL) and ribosomal nuclear (LSU / 28S) DNA sequence data. Numerous deeply-divergent clades were resolved across all markers in each of the target species, but close phylogenetic relationships - even shared haplotypes - were observed among some populations separated by large oceanic distances. Despite not being particularly buoyant, both Adenocystisutricularis and Bostrychiaintricata thus show genetic signatures of recent dispersal across vast oceanic distances, presumably by attachment to floating substrata such as wood or buoyant macroalgae. PMID:23894421

  18. Experimental evidence of a buoyant mass difference between bovine spermatozoa bearing X- and Y-chromosomes using a micromechanical resonator.

    PubMed

    Mauro, Marco; Battaglia, Raffaele; Ferrini, Gianluca; Puglisi, Roberto; Balduzzi, Donatella; Galli, Andrea

    2014-03-01

    Flow cytometry is to date the only commercially viable technique for sex preselection of mammalian spermatozoa, measuring the different DNA content in X- and Y-chromosome bearing spermatozoa. Here we present experimental evidence of a measurable difference between bovine spermatozoa bearing X- and Y-chromosomes based on their buoyant mass. Single cells of two populations of flow-cytometrically sorted spermatozoa were analyzed by means of a micromechanical resonator, consisting of a suspended doubly-clamped microcapillary. Spermatozoa buoyant mass is related to the transitory variation in vibration phase lag, caused by the passage through the sensitive area of a single sperm cell suspended in a fluid. Data analysis shows two well-separated distributions and provides evidence of the sensor capabilities to detect the buoyant mass of single cells with such accuracy to distinguish X- and Y-chromosome bearing spermatozoa. These preliminary results suggest the possibility to develop an intriguing technique alternative to flow cytometry in the field of sperm sorting. PMID:24419052

  19. Genetic Affinities between Trans-Oceanic Populations of Non-Buoyant Macroalgae in the High Latitudes of the Southern Hemisphere

    PubMed Central

    Fraser, Ceridwen I.; Zuccarello, Giuseppe C.; Spencer, Hamish G.; Salvatore, Laura C.; Garcia, Gabriella R.; Waters, Jonathan M.

    2013-01-01

    Marine biologists and biogeographers have long been puzzled by apparently non-dispersive coastal taxa that nonetheless have extensive transoceanic distributions. We here carried out a broad-scale phylogeographic study to test whether two widespread Southern Hemisphere species of non-buoyant littoral macroalgae are capable of long-distance dispersal. Samples were collected from along the coasts of southern Chile, New Zealand and several subAntarctic islands, with the focus on high latitude populations in the path of the Antarctic Circumpolar Current or West Wind Drift. We targeted two widespread littoral macroalgal species: the brown alga Adenocystisutricularis (Ectocarpales, Heterokontophyta) and the red alga Bostrychiaintricata (Ceramiales, Rhodophyta). Phylogenetic analyses were performed using partial mitochondrial (COI), chloroplast (rbcL) and ribosomal nuclear (LSU / 28S) DNA sequence data. Numerous deeply-divergent clades were resolved across all markers in each of the target species, but close phylogenetic relationships – even shared haplotypes – were observed among some populations separated by large oceanic distances. Despite not being particularly buoyant, both Adenocystisutricularis and Bostrychiaintricata thus show genetic signatures of recent dispersal across vast oceanic distances, presumably by attachment to floating substrata such as wood or buoyant macroalgae. PMID:23894421

  20. Design and evaluation of hydrophobic coated buoyant core as floating drug delivery system for sustained release of cisapride

    PubMed Central

    Jacob, Shery; Nair, Anroop B; Patil, Pandurang N

    2010-01-01

    An inert hydrophobic buoyant coated–core was developed as floating drug delivery system (FDDS) for sustained release of cisapride using direct compression technology. Core contained low density, porous ethyl cellulose, which was coated with an impermeable, insoluble hydrophobic coating polymer such as rosin. It was further seal coated with low viscosity hydroxypropyl methyl cellulose (HPMC E15) to minimize moisture permeation and better adhesion with an outer drug layer. It was found that stable buoyant core was sufficient to float the tablet more than 8 h without the aid of sodium bicarbonate and citric acid. Sustained release of cisapride was achieved with HPMC K4M in the outer drug layer. The floating lag time required for these novel FDDS was found to be zero, however it is likely that the porosity or density of the core is critical for floatability of these tablets. The in vitro release pattern of these tablets in simulated gastric fluid showed the constant and controlled release for prolonged time. It can be concluded that the hydrophobic coated buoyant core could be used as FDDS for gastroretentive delivery system of cisapride or other suitable drugs. PMID:24825997

  1. The Effects of Neutrally Buoyant, Externally Attached Transmitters on Swimming Performance and Predator Avoidance of Juvenile Chinook Salmon

    SciTech Connect

    Janak, Jill M.; Brown, Richard S.; Colotelo, Alison HA; Pflugrath, Brett D.; Stephenson, John R.; Deng, Zhiqun; Carlson, Thomas J.; Seaburg, Adam

    2012-08-01

    The presence of an externally attached telemetry tag is often associated with the potential for impaired swimming performance (i.e., snags and drag) as well as increased susceptibility to predation, specifically for smaller fish. The effects on swimming performance due to the presence of a neutrally buoyant externally attached acoustic transmitter were examined by comparing critical swimming speeds (Ucrit) for juvenile Chinook salmon tagged with two different neutrally buoyant external transmitters (Type A and B), nontagged individuals, and those surgically implanted with the current JSATS acoustic transmitter. Fish tagged with the Type A and B designs had lower Ucrit when compared to nontagged individuals. However, there was no difference in Ucrit among fish tagged with Type A or B designs compared to those with surgically implanted tags. Further testing was then conducted to determine if predator avoidance ability was affected due to the presence of Type A tags when compared to nontagged fish. No difference was detected in the number of tagged and nontagged fish consumed by rainbow trout throughout the predation trials. The results of this study support the further testing on the efficacy of a neutrally buoyant externally attached telemetry tag for survival studies involving juvenile salmonids passing through hydro turbines.

  2. Northern Monterey Bay upwelling shadow front: Observations of a coastally and surface-trapped buoyant plume

    USGS Publications Warehouse

    Woodson, C.B.; Washburn, L.; Barth, J.A.; Hoover, D.J.; Kirincich, A.R.; McManus, M.A.; Ryan, J.P.; Tyburczy, J.

    2009-01-01

    During the upwelling season in central California, northwesterly winds along the coast produce a strong upwelling jet that originates at Point A??o Nuevo and flows southward across the mouth of Monterey Bay. A convergent front with a mean temperature change of 3.77 ?? 0.29??C develops between the warm interior waters and the cold offshore upwelling jet. To examine the forcing mechanisms driving the location and movement of the upwelling shadow front and its effects on biological communities in northern Monterey Bay, oceanographic conditions were monitored using cross-shelf mooring arrays, drifters, and hydrographic surveys along a 20 km stretch of coast extending northwestward from Santa Cruz, California, during the upwelling season of 2007 (May-September). The alongshore location of the upwelling shadow front at the northern edge of the bay was driven by: regional wind forcing, through an alongshore pressure gradient; buoyancy forces due to the temperature change across the front; and local wind forcing (the diurnal sea breeze). The upwelling shadow front behaved as a surface-trapped buoyant current, which is superimposed on a poleward barotropic current, moving up and down the coast up to several kilometers each day. We surmise that the front is advected poleward by a preexisting northward barotropic current of 0.10 m s-1 that arises due to an alongshore pressure gradient caused by focused upwelling at Point A??o Nuevo. The frontal circulation (onshore surface currents) breaks the typical two-dimensional wind-driven, cross-shelf circulation (offshore surface currents) and introduces another way for water, and the material it contains (e.g., pollutants, larvae), to go across the shelf toward shore.Copyright 2009 by the American Geophysical Union.

  3. Trace Metal and Sulfur Dynamics in the First Meter of Buoyant Hydrothermal Vent Plumes

    NASA Astrophysics Data System (ADS)

    Findlay, A.; Gartman, A.; Shaw, T. J.; Luther, G. W., III

    2014-12-01

    The speciation and reactivity of metals and metal sulfides within the buoyant plume is critical to determining the ultimate fate of metals emitted from hydrothermal vents. The concentration, size fractionation, and partitioning of trace metals (Fe, Mn, Cu, Co, Zn, Cd, Pb) were determined within the first meter of the rising plume at three vent fields (TAG, Snakepit, and Rainbow) along the Mid-Atlantic Ridge. At Rainbow, total Fe concentrations exceed total sulfide concentrations by an order of magnitude, whereas at the other two sites, total Fe and total sulfide concentrations are nearly equal. At all three sites, Mn and Fe are primarily in the filtered (< 0.2 μm) fraction and Cu, Co, Zn, Cd, and Pb are mainly in the unfiltered fraction. At TAG and Snakepit, unfiltered copper is correlated with unfiltered cobalt, and unfiltered zinc is correlated with unfiltered cadmium and lead. At Rainbow, unfiltered zinc, cadmium and lead are correlated, but unfiltered copper and cobalt are not, indicating precipitation dynamics at Rainbow are different than those at TAG and Snakepit due to bulk geochemical differences, including a higher iron to sulfide ratio. A sequential HCl/HNO3 leaching method was used to distinguish metals present in pyrite and chalcopyrite in both unfiltered and filtered samples. Significant portions of unfiltered Cu and Co were extracted in HNO3, whereas unfiltered Zn, Cd, and Pb were extracted in HCl. Up to 95 % of filtered Cu, Co, and Zn, up to 80% Cd, and up to 60 % Pb are only extractable in HNO3, indicating that a significant portion of metals < 0.2 μm are incorporated into a recalcitrant fraction such as nanoparticulate pyrite or chalcopyrite.

  4. Extinction and Scattering Properties of Soot Emitted from Buoyant Turbulent Diffusion Flames. Appendix D

    NASA Technical Reports Server (NTRS)

    Krishnan, S. S.; Lin, K.-C.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Extinction and scattering properties at wavelengths of 250-5200 nm were studied for soot emitted from buoyant turbulent diffusion flames in the long residence time regime where soot properties are independent of position in the overfire region and characteristic flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propylene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered Measured scattering patterns and ratios of total scattering/absorption cross sections were in good agreement with predictions based on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visible. Measured depolarization ratios were roughly correlated by primary particle size parameter, suggesting potential for completing RDG methodology needed to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionless extinction coefficients were in good agreement with earlier measurements for similar soot populations and were independent of fuel type and wavelength except for reduced values as the near ultraviolet was approached. The ratios of the scattering/absorption refractive index functions were independent of fuel type within experimental uncertainties and were in good agreement with earlier measurements. The refractive index function for absorption was similarly independent of fuel type but was larger than earlier reflectometry measurements in the infrared. Ratios of total scattering/absorption cross sections were relatively large in the visible and near infrared, with maximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, suggesting greater potential for scattering from soot particles to affect flame radiation properties than previously thought.

  5. Extinction and Scattering Properties of Soot Emitted from Buoyant Turbulent Diffusion Flames. Appendix F

    NASA Technical Reports Server (NTRS)

    Krishnan, S. S.; Lin, K.-C.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

    2001-01-01

    Extinction and scattering properties at wavelengths of 250-5200 nm were studied for soot emitted from buoyant turbulent diffusion flames in the long residence time regime where soot properties are independent of position in the overfire region and characteristic flame residence times. Flames burning in still air and fueled with gas (acetylene, ethylene, propane, and propylene) and liquid (benzene, toluene, cyclohexane, and n-heptane) hydrocarbon fuels were considered. Measured scattering patterns and ratios of total scattering/absorption cross sections were in good agreement with predictions based on the Rayleigh-Debye-Gans (RDG) scattering approximation in the visible. Measured depolarization ratios were roughly correlated by primary particle size parameter, suggesting potential for completing RDG methodology needed to make soot scattering predictions as well as providing a nonintrusive way to measure primary soot particle diameters. Measurements of dimensionless extinction coefficients were in good agreement with earlier measurements for similar soot populations and were independent of fuel type and wavelength except for reduced values as the near ultraviolet was approached. The ratios of the scattering/absorption refractive index functions were independent of fuel type within experimental uncertainties and were in good agreement with earlier measurements. The refractive index junction for absorption was similarly independent of fuel type but was larger than earlier reflectometry measurements in the infrared. Ratios of total scattering/absorption cross sections were relatively large in the visible and near infrared, with maximum values as large as 0.9 and with values as large as 0.2 at 2000 nm, suggesting greater potential for scattering from soot particles to affect flame radiation properties than previously thought.

  6. Filament formation and evolution in buoyant coastal waters: Observation and modelling

    NASA Astrophysics Data System (ADS)

    Iermano, Ilaria; Liguori, Giovanni; Iudicone, Daniele; Buongiorno Nardelli, Bruno; Colella, Simone; Zingone, Adriana; Saggiomo, Vincenzo; Ribera d'Alcalà, Maurizio

    2012-11-01

    This paper presents a detailed analysis of the formation and subsequent evolution of filament-like structures observed in a relatively small area of the mid-Tyrrhenian Sea (Mediterranean Sea). The filament dynamics and potential impact on the cross-shelf exchange budget are investigated based on a combined use of remote sensing imagery, in situ data and numerical modelling. The complexity of these phenomena is shown by focusing on four distinct events that led to cross-shelf transport, each representative of a different dynamic process and a distinct expected impact on the coastal area. A systematic analysis of available observations for the years 1998-2006 underlines the role of the interplay of atmospheric freshwater fluxes, river loads and wind stress variations, which may create favourable conditions for the convergence of shelf waters (particularly at coastal capes) and the subsequent formation of short-lived filaments along the coast. The response of the buoyant coastal waters to periods of wind reversal and fluctuating freshwater discharge rates is examined through idealised Regional Ocean Modeling System (ROMS) simulations. The filaments observed in remote sensing imagery were well reproduced by the numerical exercise, where the filaments appear as organised submesoscale structures that possess high relative vorticity and develop at the river mouths or adjacent capes. In both scenarios, the filaments appear largely determined by (i) the presence of a buoyancy anomaly, (ii) the angle between the wind pulse direction and the coast and (iii) irregularities in the coastal profile. The ensemble of results suggests that the occurrence of such transient, intense structures may contribute considerably to the biological variability and cross-shelf exchange in coastal areas with similar traits.

  7. Dynamics of the Active Altiplano Puna Magmatic Body: Large-Scale Melt Transport and Buoyant Upwelling

    NASA Astrophysics Data System (ADS)

    Diez, M.; Del Potro, R.

    2014-12-01

    A wide range of geophysical observations suggest that an active partially molten region (Altiplano Puna Magmatic Body or APMB) lies in the mid-upper crust of the Altiplano Puna Plateau, in the Central Andes, with its upper contact at around 20 km depth. In particular, gravity, magnetotellurics and seismics have helped delineating the overall geometry of this intrusive body, which is approximately 200 km in diameter and could be many kilometers thick. The average melt fraction is poorly constrained, although it has been suggested that it could be rather high, around ~15% or higher. In addition to constraining the general shape of the APMB, its dynamics can in principle be partially accessed through geodetic measurements at the surface. In fact, recent InSAR-related studies have shown a ground deformation rate in the order of centimeter per year, with a central uplifting region, centered roughly around a lava-dome complex type of system, Uturuncu volcano, surrounded by an extensive peripheral zone of subsidence. This wealth of observations has leaded us to propose two different hypotheses to partially explain the inner workings of the APMB: (i) the dynamic deformation of the uplift-subsidence of the surface is explained by the impingement of a buoyant melt-rich blob on the more brittle upper levels of the crust, and; (ii) such surface deformation could be associated to the poroviscous compaction induced by lateral melt transport toward a central region of ascent. Both scenarios are modeled numerically. In principle the two hypotheses could explain the rate and geometry of subsidence under some simplifications. We discuss the consequences of both hypotheses, and entertain the possibility of both processes operating together.

  8. The Flow of Buoyant Meltwater Next to Ice Shelves and Icebergs

    NASA Astrophysics Data System (ADS)

    Wells, A. J.; Worster, G.

    2008-12-01

    Melting at the base of an ice shelf can play a significant role in the polar oceans, contributing to the mass balance of the ice shelf and leading to the formation of Ice Shelf Water. Fresh meltwater is relatively buoyant compared to the surrounding ocean and can rise along the ice surface, with the strength of this flow depending critically on the heat and salt fluxes from the ocean to the ice. We justify a simplified theoretical model that describes the coupling of heat and salt fluxes with the buoyancy- driven flow of meltwater, next to both vertical and sloping ice surfaces. The flow develops with distance along the ice surface, and different flow regimes can be obtained depending on the length and the slope of the ice surface. Both the heat and salt fluxes differ between the two regimes. On moderate scales the flow is controlled by buoyancy in a narrow region close to the ice surface. This predicts that the melting rate is independent of distance along the ice surface, consistent with previous laboratory scale measurements of heat transfer. This regime may be important for ablation at the sides of tabular icebergs, and under some regions of ice shelves. Further downstream, the flow is dominated by buoyancy located further from the wall, and can be described by a model similar to those often used to model ice-shelf-water plumes. This predicts that the melting rate increases with distance along the ice surface. Simple analytic solutions are also derived for flow in an unstratified fluid, which indicate the possible sensitivity of the ablation rate to changes in ocean temperature. The predicted variation of the heat and salt fluxes with distance along the ice surface may have important consequences for more complex models of ice-shelf-water flow.

  9. Buoyant Turbulent Kinetic Energy Production in Steep-Slope Katabatic Flow

    NASA Astrophysics Data System (ADS)

    Oldroyd, Holly J.; Pardyjak, Eric R.; Higgins, Chad W.; Parlange, Marc B.

    2016-07-01

    We develop several critical concepts that should be considered when interpreting, modelling and designing future experiments for flows over sloping terrain. Vertical buoyancy fluxes in katabatic flows can be positive and a source of turbulent kinetic energy (TKE) despite the statically stable, thermal stratification that drives these flows. This phenomenon occurs when the ratio of along-slope to slope-normal kinematic heat fluxes is greater than the cotangent of the slope angle, suggesting a critical value of slope-angle steepness found in earlier studies. We provide field-data-based evidence that the along-slope heat flux may dominate the variables in this inequality, and therefore in generating buoyant TKE production or suppression over a steep slope. These data show the along-slope heat flux can be more variable and significantly larger in magnitude than the slope-normal component. The gradient Richardson number does not include the effects of the along-slope buoyancy; furthermore, none of the canonical stability parameters can properly reflect the TKE redistribution from turbulent transport divergence and the sink of TKE in cases of counter-gradient momentum fluxes, which we frequently observe near the peak of the katabatic jet. In such cases, canonical stability parameters inadequately represent the physical mechanisms associated with stability. These results have broad implications related to accurately modelling turbulence and surface exchanges over sloping terrain and illustrate the need to more thoroughly investigate the along-slope heat flux and its drivers, the meaning and definitions of stability, and the effects of non-local turbulent transport.

  10. Trench Advance By the Subduction of Buoyant Features - Application to the Izu-Bonin-Marianas Arc

    NASA Astrophysics Data System (ADS)

    Goes, S. D. B.; Fourel, L.; Morra, G.

    2014-12-01

    Most subduction trenches retreat, not only today but throughout the Cenozoic. However, a few trenches clearly advance during part of the evolution, including Izu-Bonin Marianas (IBM) and Kermadec. Trench retreat is well understood as a basic consequence of slab pull, but it is debated what causes trench advance. The IBM trench underwent a complex evolution: right after its initiation, it rotated clockwise, leading to very fast retreat in the north and slow retreat in the south. But since 10-15 Ma, IBM trench motions have switched to advance at the southern end, and since 5 Ma also the northern end is advancing. Based on 2-D subduction models, it has been proposed proposed that the change in age of the subducting plate at the IBM trench (from 40-70 m.y. at the initiation of the trench 45 m.y. ago to 100-140 m.y. lithosphere subducting at the trench today) and its effect on plate strength could explain the transition from trench retreat to trench advance, and that the age gradient (younger in the north and older in the south) could explain the rotation of the trench. However, with new 3-D coupled fluid-solid subduction model where we can include such lateral age gradients, we find that this does not yield the observed behaviour. Instead, we propose an alternative mechanism, involving the subduction of the buoyant Caroline Island Ridge at the southern edge of the Mariana trench and show that it can explain both trench motion history and the current morphology of the IBM slab as imaged by seismic tomography.

  11. Vortex-induced vibrations of a neutrally buoyant circular cylinder near a plane wall

    NASA Astrophysics Data System (ADS)

    Wang, X. K.; Hao, Z.; Tan, S. K.

    2013-05-01

    This paper presents an experimental study of the motions, drag force and vortex shedding patterns of an elastically mounted circular cylinder, which is held at various heights above a plane wall and is subject to vortex-induced vibration (VIV) in the transverse direction. The cylinder is neutrally buoyant with a mass ratio m=1.0 and has a low damping ratio ζ=0.0173. Effects of the gap ratio (S/D) ranged from 0.05 to 2.5 and the free-stream velocity (U) ranged from 0.15 to 0.65m/s (corresponding to 3000≤Re≤13 000, and 1.53≤U≤6.62) are examined. The flow around the cylinder has been measured using particle image velocimetry (PIV), in conjunction with direct measurements of the dynamic drag force on the cylinder using a piezoelectric load cell. Results of the vibrating cylinder under unbounded (or free-standing) condition, as well as those of a near-wall stationary cylinder at the same gap ratios, are also provided. For the free-standing cylinder, the transition from the initial branch to the upper branch is characterized by a switch of vortex pattern from the classical 2S mode to the newly-discovered 2PO mode by Morse and Williamson (2009). The nearby wall not only affects the amplitude and frequency of vibration, but also leads to non-linearities in the cylinder response as evidenced by the presence of super-harmonics in the drag force spectrum. In contrast to the case of a stationary cylinder that vortex shedding is suppressed below a critical gap ratio (S/D≈0.3), the elastically mounted cylinder always vibrates even at the smallest gap ratio S/D=0.05. Due to the proximity of the plane wall, the vortices shed from the vibrating cylinder that would otherwise be in a double-sided vortex street pattern (either 2S or 2PO mode) under free-standing condition are arranged into a single-sided pattern.

  12. Two-phase convective mixing under a buoyant plume of CO2 in deep saline aquifers

    NASA Astrophysics Data System (ADS)

    Emami-Meybodi, Hamid; Hassanzadeh, Hassan

    2015-02-01

    The storage of carbon dioxide (CO2) in deep saline aquifers has been suggested as a promising method for stabilizing the atmospheric concentration of CO2. An accurate evaluation of the CO2 trapping mechanisms, such as convective mixing, is crucial for estimates of storage capacity and security. We recently investigated the gravitational stability of the diffusive boundary layer underneath a capillary transition zone by performing a linear stability analysis, which provides a quantitative description of the onset of convection for the two-phase, buoyancy-driven flow in the presence of the capillary transition zone (Emami-Meybodi and Hassanzadeh, 2013). In this paper, we further examine the effect of the capillary transition zone on the onset of convection and subsequent convective mixing using direct numerical simulations. We describe key features of the two-phase convective mixing for systems with low Rayleigh numbers (Ra ≤ 1000) and the measurement of several global quantities, such as the total CO2 dissolution, Sherwood number, swelling factor, and interface velocity. We show that the commonly used assumption of a sharp CO2-brine interface with constant CO2 concentration at the top of an aquifer (i.e. single-phase system) may lead to erroneous estimates of not only the onset of convection, but also of the rate and magnitude of CO2 dissolution. The significant effect of the capillary transition zone on the dissolution of CO2 under a buoyant plume in saline aquifers is explained; and, the link between the capillary transition zone and the volume change, due to CO2 dissolution and the interface velocity over the mixing process, is demonstrated. Compared to the single-phase system, a crossflow through the interface of the diffusive boundary layer with the capillary transition zone, as well as the upward advance of the interface motion, may enhance the convective mixing early in the period of natural convection. The decrease in the onset time and stronger mass flux

  13. The Zigzag Path of Buoyant Magnetic Tubes and the Generation of Vorticity along Their Periphery

    NASA Astrophysics Data System (ADS)

    Emonet, T.; Moreno-Insertis, F.; Rast, M. P.

    2001-03-01

    We study the generation of vorticity in the magnetic boundary layer of buoyant magnetic tubes and its consequences for the trajectory of magnetic structures rising in the solar convection zone. When the Reynolds number is well above 1, the wake trailing the tube sheds vortex rolls, producing a von Kármán vortex street, similar to the case of flows around rigid cylinders. The shedding of a vortex roll causes an imbalance of vorticity in the tube. The ensuing vortex force excites a transverse oscillation of the flux tube as a whole so that it follows a zigzag upward path instead of rising along a straight vertical line. In this paper, the physics of vorticity generation in the boundary layer is discussed and scaling laws for the relevant terms are presented. We then solve the two-dimensional magnetohydrodynamic equations numerically, measure the vorticity production, and show the formation of a vortex street and the consequent sinusoidal path of the magnetic flux tube. For high values of the plasma beta, the trajectory of the tubes is found to be independent of β but varying with the Reynolds number. The Strouhal number, which measures the frequency of vortex shedding, shows in our rising tubes only a weak dependence with the Reynolds numbers, a result also obtained in the rigid-tube laboratory experiments. In fact, the actual values measured in the latter are also close to those of our numerical calculations. As the Reynolds numbers are increased, the amplitude of the lift force grows and the trajectory becomes increasingly complicated. It is shown how a simple analytical equation (which includes buoyancy, drag, and vortex forces) can satisfactorily reproduce the computed trajectories. The different regimes of rise can be best understood in terms of a dimensionless parameter, χ, which measures the importance of the vortex force as compared with the buoyancy and drag forces. For χ2<<1, the rise is drag dominated and the trajectory is mainly vertical with a small

  14. Localized Density Instabilities Driven By Interface Shear and Their Influence on Removal of Sediment from Buoyant Plumes

    NASA Astrophysics Data System (ADS)

    Rouhnia, M.; Strom, K.

    2015-12-01

    Sediment removal rates from buoyant river discharges are typically scaled with particle settling velocity. However, some field and laboratory data suggest that removal can take place at rates higher than those predicted by individual particle settling. It is possible that these enhanced removal rates could potentially be due, at least in part, to mass settling of fluid and sediment near the fresh and saltwater interface. Fluid shear at the interface can mix the freshwater and sediment with the underlying saltwater and lead to pockets or bands of saltwater and sediment that are more dense than the underlying clear saltwater; resulting in an unstable configuration that can lead to rapid vertical transport of sediment. In this study, we perform laboratory experiments to study the enhancement of sediment removal from buoyant plumes under the effect of shear-driven gravitational instabilities. To do this, we ran a 5 cm deep layer of freshwater with flocculated kaolinite over a 50 cm deep basin of clear saltwater in a 1 m long glass flume under a range of upper layer velocities, concentrations, and initial stratification ratios. A Vectrino profiler is placed such that it constantly records velocity profiles from 2 cm above to 2 cm below the original interface. The velocity of the buoyant layer is controlled using a vertical head pipe at the flume inlet, and the Richardson number is varied from 0.05 to 0.25. The interface is monitored with a digital camera and a laser sheet, and Rhodamine B is added to the buoyant layer for better visualization. Snapshots from the video are used to observe the overall dynamics and developments of instabilities at the interface. The sediment concentration of the inflow and outflow of the system are continuously measured with a pair of OBS sensors, and floc size is measured with a floc imaging system and converted to a floc settling velocity. The difference in sediment concentration between the two OBS sensors is used along with a mass

  15. Use of a Force Sensor in Archimedes' Principle Experiment, Determination of Buoyant Force and Acceleration Due To Gravity

    NASA Astrophysics Data System (ADS)

    Aurora, Tarlok

    2013-04-01

    In introductory physics, students verify Archimedes' principle by immersing an object in water in a container, with a side-spout to collect the displaced water, resulting in a large uncertainty, due to surface tension. A modified procedure was introduced, in which a plastic bucket is suspended from a force sensor, and an object hangs underneath the bucket. The object is immersed in water in a glass beaker (without any side spout), and the weight loss is measured with a computer-controlled force sensor. Instead of collecting the water displaced by the object, tap water was added to the bucket to compensate for the weight loss, and the Archimedes' principle was verified within less than a percent. With this apparatus, buoyant force was easily studied as a function of volume of displaced water; as well as a function of density of saline solution. By graphing buoyant force as a function of volume (or density of liquid), value of g was obtained from slope. Apparatus and sources of error will be discussed.

  16. Synthesis of buoyant metal-coated fly ash cenosphere and its excellent catalytic performance in dye degradation.

    PubMed

    Wang, Wei; Zhai, Jianping; Li, Qin

    2015-04-15

    In this work, Ag(+) and Ag(0) were absorbed onto the surface of 3-mercaptopropyltriethoxysilane modified fly ash cenospheres (FACs) in two Ag activation processes. The activation methods, avoiding traditional surface sensitization by SnCl2, successfully initiated electroless copper particles deposition for the preparation of buoyant Cu-FAC and CuAg-FAC composites. The CuAg-FAC had a much more uniform morphology than the Cu-FAC. The catalytic performance of the Cu-FAC and CuAg-FAC was examined by the reduction of Orange IV azo dye with the presence of NaBH4. 98.4% of Orange IV was rapidly reduced within 25 min by the CuAg-FAC, whereas 76.4% of Orange IV was removed by the Cu-FAC. The results reveal that the degradation processes matched well with the pseudo-first-order kinetics model, and rate constants of 0.057 and 0.186 min(-1) were obtained for the Cu-FAC and CuAg-FAC, respectively. Moreover, two other dyes of Orange II and Reactive Black 5 were also efficiently reduced by the CuAg-FAC which could be easily recycled and stably reused at least four times. These buoyant metal-coated FAC composites would be very useful in various catalytic reductions. PMID:25585281

  17. A hybrid approach for the simulation of a nearly neutrally buoyant nanoparticle thermal motion in an incompressible Newtonian fluid medium.

    PubMed

    Uma, B; Radhakrishnan, R; Eckmann, D M; Ayyaswamy, P S

    2013-01-01

    A hybrid scheme based on Markovian fluctuating hydrodynamics of the fluid and a non-Markovian Langevin dynamics with the Ornstein-Uhlenbeck noise perturbing the translational and rotational equations of motion of a nanoparticle is employed to study the thermal motion of a nearly neutrally buoyant nanoparticle in an incompressible Newtonian fluid medium. A direct numerical simulation adopting an arbitrary Lagrangian-Eulerian based finite element method is employed in simulating the thermal motion of the particle suspended in the fluid contained in a cylindrical vessel. The instantaneous flow around the particle and the particle motion are fully resolved. The numerical results show that (a) the calculated temperature of the nearly neutrally buoyant Brownian particle in a quiescent fluid satisfies the equipartition theorem; (b) the translational and rotational decay of the velocity autocorrelation functions result in algebraic tails, over long time; (c) the translational and rotational mean square displacements of the particle obeys Stokes-Einstein and Stokes-Einstein-Debye relations, respectively; and (d) the parallel and perpendicular diffusivities of the particle closer to the wall are consistent with the analytical results, where available. The study has important implications for designing nanocarriers for targeted drug delivery. PMID:23814315

  18. Numerical study of a buoyant plume from a multi-flue stack into a variable temperature gradient atmosphere.

    PubMed

    Velamati, Ratna Kishore; Vivek, M; Goutham, K; Sreekanth, G R; Dharmarajan, Santosh; Goel, Mukesh

    2015-11-01

    Air pollution is one of the major global hazards and industries have been one of its major contributors. This paper primarily focuses on analyzing the dispersion characteristics of buoyant plumes of the pollutant released from a multi-flue vertical stack into a variable temperature gradient atmosphere (α) in a constant-velocity cross wind using two stack configurations-inline and parallel. The study is conducted for different Froude numbers, Fr = 12.64, 9.55, and 8.27. The atmospheric temperature gradients considered for the study are 0, +1, +1.5, and +2 K/100 m. The numerical study is done using the commercial computational fluid dynamics (CFD) code FLUENT. The effects of stack configuration, α, and Fr on the plume characteristics are presented. It is observed that the plume rises higher and disperses over a larger area with the inline configuration due to better mixing and shielding effect. With higher α, it is seen that the plume rises initially and then descends due to variation of the buoyant force. The plume rise initially is strongly influenced by the momentum of the jet, and as it moves downstream, it is influenced by the cooling rate of the plume. Furthermore, the plume rises higher and disperses over a larger area with a decrease in Fr. PMID:26099599

  19. The influence of buoyant convection on the nucleation of n-propanol in thermal diffusion cloud chambers.

    PubMed

    Ferguson, Frank T; Heist, Richard H; Nuth, Joseph A

    2010-05-28

    A two-dimensional numerical model has been applied to three thermal diffusion cloud chamber (TDCC) investigations of n-propanol in helium taken by two different research groups to provide a quantitative example of how the results in these chambers can be affected by buoyant convection. In the first set of TDCC data, corrections for buoyancy resolve an apparent discontinuity in critical supersaturation data and also yield nucleation rate data that tend to agree better with higher rate, expansion-based studies at the same temperature. In the second TDCC study, the nucleation of propanol was studied over an extended pressure range. When the model was applied to these data, the possible variation in supersaturation values due to convection induced by conditions at the chamber sidewall was found to be comparable in magnitude to the experimentally observed range and may be responsible for some of this observed pressure dependence. In the third TDCC study, the combination of an error in a transport property and buoyant convection appear responsible for a perceived pressure effect in the experimental data. After correcting for this transport property and for buoyancy, the results at higher temperatures agree quite closely with the predictions of classical nucleation theory. PMID:20515103

  20. Self Induced Buoyant Blow Off in Upward Flame Spread on Thin Solid Fuels

    NASA Technical Reports Server (NTRS)

    Johnston, Michael C.; T'ien, James S.; Muff, Derek E.; Olson, Sandra L.; Ferkul, Paul V.

    2013-01-01

    ) is as follows: The observed one-sided extinction is a blow- off induced by buoyant entrainment. It is known that the flammable diffusion flame regime is bounded by quenching and blow ]off limits when varying incoming air velocity. The narrowest samples tested (between 2 and 5 cm) begin within the flammable range, but as the flame grows, the buoyancy driven air velocity increases at the neighborhood of the flame base. The initially stable flame crosses the extinguishment boundary resulting in a flame blow-off. When one-side of the flame extinguishes, the remaining side shrinks due to the reduced heat transfer to the solid. This reduces the induced velocity and the flame becomes stable. It is proposed that this may have implications to upward flame growth beyond this experiment.

  1. Axi-asymmetric development of buoyant diapirs in analogue and numerical experiments: the role of source-layer tilts

    NASA Astrophysics Data System (ADS)

    Dutta, Urmi; Baruah, Amiya; Mandal, Nibir

    2016-04-01

    Diapiric structure owing to gravity instabilities, triggered by density inversion in the rock sequences, is a unique geodynamic manifestation. High-density layers that rest upon low-density layers tend to sink, forcing the latter to squeeze up in the form of domal shapes, called buoyant diapirs. Using two-layer viscous model experiments, we investigated the effects of source-layer tilt (β) in controlling the ascent behaviour of buoyant diapirs initiated by a Rayleigh-Taylor instability. Results from our laboratory experiments, performed with a buoyant viscous layer (PDMS; density: 965.0 kg/m3) underlying a denser fluid (water; density: 998.2 kg/m3) suggest that the diapir shape is highly sensitive to β. The results suggest that diapirs growing from a tilted source layer ascend with contrasting lateral spreading rates in the up and down slope directions, resulting in axi-asymmetric geometry. Conversely, diapirs initiated from a horizontal source layer always maintain axi- symmetric shape as they grow. Interestingly, diapir heads retain a circular outline on the horizontal top surface irrespective of their degree of symmetry. However, for the axi-asymmetric cases, the upwelling axis is shifted more in the up-slope direction, i.e. away from the centre of this circular geometry. We show a spectrum of the axi-symmetric to -asymmetric geometrical transitions as a function of the source-layer tilt (β). For large β (> 4o), the diapirs become unstable, and their stems undergo a continuous drift in the upslope direction during their vertical growth. Whilst, several studies have shown the development of axi-asymmetric diapirs, the underlain flow kinematics in the viscous layers as a function of source layer tilt leading to such shape transition remains unclear. With this objective we ran computational fluid dynamic (CFD) simulations, by employing the volume of fluid (VOF) method, to investigate the role of underlying dynamics for axi-asymmetric diapiric growth. This study

  2. Rates of photocatalytic oxidation of crude oil on salt water on buoyant, cenosphere-attached titanium dioxide

    SciTech Connect

    Nair, M.; Luo, Zhenghao; Heller, A. )

    1993-10-01

    The rate of TiO[sub 2]-photocatalyzed oxidation of crude oils spilled on aqueous 0.5 M NaCA was determined by measuring the rate of O[sub 2] uptake. The photocatalyst was attached to 100-[mu]m-diameter fly-ash-derived buoyant cenospheres. Partial hydrophobic coating of the cenospheres assured their retention at the air-oil interface. The rate depended on the near-UV (broad band, 365-nm peak) irradiance below 25W m[sup [minus]2], but varied only mildly with irradiance in the 25-45 W m[sup [minus]2] range. It increased upon wave motion imitating agitation of the liquid, and upon increase of the cenosphere:oil mass ratio. It varied only mildly for different crudes. From the measured rates, cleanup times as short as 5-10 days were estimated.

  3. Relation between shape of liquid-gas interface and evolution of buoyantly unstable three-dimensional chemical fronts.

    PubMed

    Sebestíková, L

    2013-09-01

    Buoyantly unstable 3D chemical fronts were seen traveling through an iodate-arsenous acid reaction solution. The experiments were performed in channel reactors with rectangular cross sections, where the top of the reaction solution was in contact with air. A concave or convex meniscus was pinned to reactor lateral walls. Influence of the meniscus shape on front development was investigated. For the concave meniscus, an asymptotic shape of fronts holding negative curvature was observed. On the other hand, fronts propagating in the solution with the convex meniscus kept only positive curvature. Those fronts were also a bit faster than fronts propagating in the solution with the concave meniscus. A relation between the meniscus shape, flow distribution, velocity, and shape is discussed. PMID:24125360

  4. Robust spatially resolved pressure measurements using MRI with novel buoyant advection-free preparations of stable microbubbles in polysaccharide gels

    NASA Astrophysics Data System (ADS)

    Morris, Robert H.; Bencsik, Martin; Nestle, Nikolaus; Galvosas, Petrik; Fairhurst, David; Vangala, Anil; Perrie, Yvonne; McHale, Glen

    2008-08-01

    MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25 min. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-distearoyl- sn-glycero-3-phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44 bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar.

  5. 46 CFR 160.060-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

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  6. 46 CFR 160.047-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 6 2010-10-01 2010-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.047-3a Section 160.047-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  7. 46 CFR 160.060-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 6 2011-10-01 2011-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.060-3a Section 160.060-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  8. 46 CFR 160.052-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 6 2011-10-01 2011-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.052-3a Section 160.052-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  9. 46 CFR 160.052-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 6 2010-10-01 2010-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.052-3a Section 160.052-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  10. 46 CFR 160.047-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 6 2011-10-01 2011-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.047-3a Section 160.047-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  11. 46 CFR 160.047-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 6 2013-10-01 2013-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.047-3a Section 160.047-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  12. 46 CFR 160.052-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 6 2013-10-01 2013-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.052-3a Section 160.052-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  13. 46 CFR 160.052-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 6 2014-10-01 2014-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.052-3a Section 160.052-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  14. 46 CFR 160.047-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 6 2014-10-01 2014-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.047-3a Section 160.047-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  15. 46 CFR 160.060-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 6 2014-10-01 2014-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.060-3a Section 160.060-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  16. 46 CFR 160.060-3a - Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 6 2013-10-01 2013-10-01 false Materials-Dee ring and snap hook assemblies and other instruments of closure for buoyant vests. 160.060-3a Section 160.060-3a Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) EQUIPMENT, CONSTRUCTION, AND MATERIALS: SPECIFICATIONS AND APPROVAL LIFESAVING EQUIPMENT Specification for...

  17. A Field Evaluation of an External and Neutrally Buoyant Acoustic Transmitter for Juvenile Salmon: Implications for Estimating Hydroturbine Passage Survival

    PubMed Central

    Brown, Richard S.; Deng, Z. Daniel; Cook, Katrina V.; Pflugrath, Brett D.; Li, Xinya; Fu, Tao; Martinez, Jayson J.; Li, Huidong; Trumbo, Bradly A.; Ahmann, Martin L.; Seaburg, Adam G.

    2013-01-01

    Turbine-passed fish are exposed to rapid decreases in pressure which can cause barotrauma. The presence of an implanted telemetry tag increases the likelihood of injury or death from exposure to pressure changes, thus potentially biasing studies evaluating survival of turbine-passed fish. Therefore, a neutrally buoyant externally attached tag was developed to eliminate this bias in turbine passage studies. This new tag was designed not to add excess mass in water or take up space in the coelom, having an effective tag burden of zero with the goal of reducing pressure related biases to turbine survival studies. To determine if this new tag affects fish performance or susceptibility to predation, it was evaluated in the field relative to internally implanted acoustic transmitters (JSATS; Juvenile Salmon Acoustic Telemetry System) used widely for survival studies of juvenile salmonids. Survival and travel time through the study reach was compared between fish with either tag type in an area of high predation in the Snake and Columbia rivers, Washington. An additional group of fish affixed with neutrally-buoyant dummy external tags were implanted with passive integrated transponder (PIT) tags and recovered further downstream to assess external tag retention and injury. There were no significant differences in survival to the first detection site, 12 river kilometers (rkm) downstream of release. Travel times were also similar between groups. Conversely, externally-tagged fish had reduced survival (or elevated tag loss) to the second detection site, 65 rkm downstream. In addition, the retention study revealed that tag loss was first observed in fish recaptured approximately 9 days after release. Results suggest that this new tag may be viable for short term (<8 days) single-dam turbine-passage studies and under these situations, may alleviate the turbine passage-related bias encountered when using internal tags, however further research is needed to confirm this. PMID

  18. A field evaluation of an external and neutrally buoyant acoustic transmitter for juvenile salmon: implications for estimating hydroturbine passage survival.

    PubMed

    Brown, Richard S; Deng, Z Daniel; Cook, Katrina V; Pflugrath, Brett D; Li, Xinya; Fu, Tao; Martinez, Jayson J; Li, Huidong; Trumbo, Bradly A; Ahmann, Martin L; Seaburg, Adam G

    2013-01-01

    Turbine-passed fish are exposed to rapid decreases in pressure which can cause barotrauma. The presence of an implanted telemetry tag increases the likelihood of injury or death from exposure to pressure changes, thus potentially biasing studies evaluating survival of turbine-passed fish. Therefore, a neutrally buoyant externally attached tag was developed to eliminate this bias in turbine passage studies. This new tag was designed not to add excess mass in water or take up space in the coelom, having an effective tag burden of zero with the goal of reducing pressure related biases to turbine survival studies. To determine if this new tag affects fish performance or susceptibility to predation, it was evaluated in the field relative to internally implanted acoustic transmitters (JSATS; Juvenile Salmon Acoustic Telemetry System) used widely for survival studies of juvenile salmonids. Survival and travel time through the study reach was compared between fish with either tag type in an area of high predation in the Snake and Columbia rivers, Washington. An additional group of fish affixed with neutrally-buoyant dummy external tags were implanted with passive integrated transponder (PIT) tags and recovered further downstream to assess external tag retention and injury. There were no significant differences in survival to the first detection site, 12 river kilometers (rkm) downstream of release. Travel times were also similar between groups. Conversely, externally-tagged fish had reduced survival (or elevated tag loss) to the second detection site, 65 rkm downstream. In addition, the retention study revealed that tag loss was first observed in fish recaptured approximately 9 days after release. Results suggest that this new tag may be viable for short term (<8 days) single-dam turbine-passage studies and under these situations, may alleviate the turbine passage-related bias encountered when using internal tags, however further research is needed to confirm this. PMID

  19. The Buoyant Filter Bioreactor: a high-rate anaerobic reactor for complex wastewater--process dynamics with dairy effluent.

    PubMed

    Haridas, Ajit; Suresh, S; Chitra, K R; Manilal, V B

    2005-03-01

    A novel high-rate anaerobic reactor, called "Buoyant Filter Bioreactor" (BFBR), has been developed for treating lipid-rich complex wastewater. The BFBR is able to decouple the biomass and insoluble COD retention time from the hydraulic retention time by means of a granular filter bed made of buoyant polystyrene beads. Filter clogging is prevented by an automatic backwash driven by biogas release, which fluidizes the granular filter bed in a downward direction. During filter backwash, the solids captured in the filter are reintroduced into the reaction zone of the reactor. The reaction zone is provided with a mixing system, which is independent of the hydraulic retention time. The performance of a laboratory-scale BFBR was studied for the treatment of dairy effluent, chosen as a model complex wastewater. The dairy effluent was not pre-treated for fat removal. The BFBR was operated over 400 d and showed greater than 85% COD removal at 10 kg COD/(m3/d). The COD conversion to methane in the BFBR was essentially complete. The BFBR performance improved with age, and with feed containing 3200 mg COD/l, the treated effluent had 120 mg COD/l and no turbidity. The hold-up of degradable biosolids, including scum, inside the BFBR was estimated using starvation tests. When load is increased, scum accumulates inside the BFBR and then decays after undergoing change from hydrophobic to hydrophilic. This is explained as the accumulation of fat solids, its conversion to insoluble long chain fatty acids and its further solubilization and degradation. PMID:15766954

  20. Physiological considerations in applying laboratory-determined buoyant densities to predictions of bacterial and protozoan transport in groundwater: Results of in-situ and laboratory tests

    USGS Publications Warehouse

    Harvey, R.W.; Metge, D.W.; Kinner, N.; Mayberry, N.

    1997-01-01

    Buoyant densities were determined for groundwater bacteria and microflagellates (protozoa) from a sandy aquifer (Cape Cod, MA) using two methods: (1) density-gradient centrifugation (DGC) and (2) Stoke's law approximations using sedimentation rates observed during natural-gradient injection and recovery tests. The dwarf (average cell size, 0.3 ??m), unattached bacteria inhabiting a pristine zone just beneath the water table and a majority (~80%) of the morphologically diverse community of free- living bacteria inhabiting a 5-km-long plume of organically-contaminated groundwater had DGC-determined buoyant densities <1.019 g/cm3 before culturing. In the aquifer, sinking rates for the uncultured 2-??m size class of contaminant plume bacteria were comparable to that of the bromide tracer (1.9 x 10-3 M), also suggesting a low buoyant density. Culturing groundwater bacteria resulted in larger (0.8-1.3 ??m), less neutrally- buoyant (1.043-1.081 g/cm3) cells with potential sedimentation rates up to 64-fold higher than those predicted for the uncultured populations. Although sedimentation generally could be neglected in predicting subsurface transport for the community of free-living groundwater bacteria, it appeared to be important for the cultured isolates, at least until they readapt to aquifer conditions. Culturing-induced alterations in size of the contaminant-plume microflagellates (2-3 ??m) were ameliorated by using a lower nutrient, acidic (pH 5) porous growth medium. Buoyant densities of the cultured microflagellates were low, i.e., 1.024-1.034 g/cm3 (using the DGC assay) and 1.017-1.039 g/cm3 (estimated from in-situ sedimentation rates), suggesting good potential for subsurface transport under favorable conditions.

  1. Experimental Study on Basic Shape of Simple Device for Prevention of Inflow and Accumulation of Buoyant Refuse at the Intake of Headworks

    NASA Astrophysics Data System (ADS)

    Namihira, Atsushi; Kobayashi, Hiroyasu; Takaki, Kyoji; Goto, Masahiro

    In this research, the basic shape of the device for prevention of inflow and accumulation of buoyant refuse at the intake of headworks is investigated by hydraulic model test. As results, it is clarified that an enough result is not obtained if the prismatic bar that floats on the water is set as the device for prevention so that it may cross the intake. On the other hands, it is clarified that the inflow and accumulation of buoyant refuse at the intake is decreased greatly if the bar is set so that it may be diagonally thrust out from the upstream edge of the intake to the downstream on the river side. In this case, it is necessary to decide the length and setting angle of the bar so that it may intersect with the boundary line of the area where the refuse flow into the intake with no device for prevention.

  2. In-situ optical and acoustical measurements of the buoyant cyanobacterium p. Rubescens: spatial and temporal distribution patterns.

    PubMed

    Hofmann, Hilmar; Peeters, Frank

    2013-01-01

    Optical (fluorescence) and acoustic in-situ techniques were tested in their ability to measure the spatial and temporal distribution of plankton in freshwater ecosystems with special emphasis on the harmful and buoyant cyanobacterium P. rubescens. Fluorescence was measured with the multi-spectral FluoroProbe (Moldaenke FluoroProbe, MFP) and a Seapoint Chlorophyll Fluorometer (SCF). In-situ measurements of the acoustic backscatter strength (ABS) were conducted with three different acoustic devices covering multiple acoustic frequencies (614 kHz ADCP, 2 MHz ADP, and 6 MHz ADV). The MFP provides a fast and reliable technique to measure fluorescence at different wavelengths in situ, which allows discriminating between P. rubescens and other phytoplankton species. All three acoustic devices are sensitive to P. rubescens even if other scatterers, e.g., zooplankton or suspended sediment, are present in the water column, because P. rubescens containing gas vesicles has a strong density difference and hence acoustic contrast to the ambient water and other scatterers. After calibration, the combination of optical and acoustical measurements not only allows qualitative and quantitative observation of P. rubescens, but also distinction between P. rubescens, other phytoplankton, and zooplankton. As the measuring devices can sample in situ at high rates they enable assessment of plankton distributions at high temporal (minutes) and spatial (decimeters) resolution or covering large temporal (seasonal) and spatial (basin scale) scales. PMID:24303028

  3. Axial allometry in a neutrally buoyant environment: effects of the terrestrial-aquatic transition on vertebral scaling.

    PubMed

    Jones, K E; Pierce, S E

    2016-03-01

    Ecological diversification into new environments presents new mechanical challenges for locomotion. An extreme example of this is the transition from a terrestrial to an aquatic lifestyle. Here, we examine the implications of life in a neutrally buoyant environment on adaptations of the axial skeleton to evolutionary increases in body size. On land, mammals must use their thoracolumbar vertebral column for body support against gravity and thus exhibit increasing stabilization of the trunk as body size increases. Conversely, in water, the role of the axial skeleton in body support is reduced, and, in aquatic mammals, the vertebral column functions primarily in locomotion. Therefore, we hypothesize that the allometric stabilization associated with increasing body size in terrestrial mammals will be minimized in secondarily aquatic mammals. We test this by comparing the scaling exponent (slope) of vertebral measures from 57 terrestrial species (23 felids, 34 bovids) to 23 semi-aquatic species (pinnipeds), using phylogenetically corrected regressions. Terrestrial taxa meet predictions of allometric stabilization, with posterior vertebral column (lumbar region) shortening, increased vertebral height compared to width, and shorter, more disc-shaped centra. In contrast, pinniped vertebral proportions (e.g. length, width, height) scale with isometry, and in some cases, centra even become more spool-shaped with increasing size, suggesting increased flexibility. Our results demonstrate that evolution of a secondarily aquatic lifestyle has modified the mechanical constraints associated with evolutionary increases in body size, relative to terrestrial taxa. PMID:26679743

  4. Algal Parasite Herpodiscus durvillaeae (Phaeophyceae: Sphacelariales) Inferred to have Traversed the Pacific Ocean with its Buoyant Host.

    PubMed

    Fraser, Ceridwen I; Waters, Jonathan M

    2013-02-01

    The parasitic phaeophycean endophyte Herpodiscus durvillaeae (Lindauer) G. R. South has previously only been recorded from New Zealand, in association with a single host species, Durvillaea antarctica (Chamisso) Hariot (southern bull-kelp). Here we use DNA sequence data from plastid and nuclear markers (chloroplast rbcL, ribosomal LSU, and a nuclear pseudogene copy of COI) to test for the presence of H. durvillaeae beyond the New Zealand region, and on host species other than D. antarctica. Analyses of samples from the Falkland Islands confirm the first record of H. durvillaeae from the Atlantic Ocean. We report that Falkland Islands H. durvillaeae are genetically indistinguishable from samples of this species from New Zealand's sub-Antarctic Campbell Island, suggesting recent dispersal of the parasite across the Pacific Ocean, presumably by rafting with its buoyant macroalgal host. We also here record H. durvillaeae from New Zealand endemics Durvillaea poha Fraser et al. and D. willana Lindauer. PMID:27008401

  5. A novel technique to neutralize the Yawing moment due to asymmetric thrust in a hybrid buoyant aircraft

    NASA Astrophysics Data System (ADS)

    Haque, Anwar U.; Asrar, Waqar; Omar, Ashraf A.; Sulaeman, Erwin; J. S Ali, Mohamed

    2016-03-01

    Dorsal fin is used in swimming animals like shark for the generation of thrust as well as to meet the requirement of the lateral stability. In the case of aircraft, rudders are normally used for the said requirement. In the present work, this nature inspired idea is explored for its application to neutralize the unavoidable asymmetric thrust produced by the twin engines of a hybrid buoyant aircraft. First, the estimation of asymmetric thrust is obtained with the help of analytical techniques for maximum thrust condition at 4 degree angle of attack. The moment generated by it is utilized for the sizing of a dorsal fin which looks similar to a tapered wing and is placed aft of the center of gravity. Wind tunnel testing at subsonic speed is carried out to explore the design features of this rotatable dorsal fin. It is found that a small rotation of 5 degree can generate the required moment. However, such rotation requires a complete pneumatic/electro-mechanical system and an alternative of it is to use a cambered airfoil for the dorsal fin installed at fixed location. Such a flow controlling device can also be used as an antenna mast, which is commonly installed out the fuselage of the aircraft for communication purposes. Moreover, by incorporating this technique, a pilot doesn't have to put an extra effort to make the aircraft stable in the presence of side wind.

  6. Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers.

    PubMed

    Rosén, T; Einarsson, J; Nordmark, A; Aidun, C K; Lundell, F; Mehlig, B

    2015-12-01

    We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Re(a). As Re(a)→0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Re(a) for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio λ(c)≈0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the λ-Re(a) plane that reaches λ≈0.1275 at the smallest shear Reynolds number (Re(a)=1) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results. PMID:26764819

  7. In-Situ Optical and Acoustical Measurements of the Buoyant Cyanobacterium P. Rubescens: Spatial and Temporal Distribution Patterns

    PubMed Central

    Hofmann, Hilmar; Peeters, Frank

    2013-01-01

    Optical (fluorescence) and acoustic in-situ techniques were tested in their ability to measure the spatial and temporal distribution of plankton in freshwater ecosystems with special emphasis on the harmful and buoyant cyanobacterium P. rubescens. Fluorescence was measured with the multi-spectral FluoroProbe (Moldaenke FluoroProbe, MFP) and a Seapoint Chlorophyll Fluorometer (SCF). In-situ measurements of the acoustic backscatter strength (ABS) were conducted with three different acoustic devices covering multiple acoustic frequencies (614 kHz ADCP, 2 MHz ADP, and 6 MHz ADV). The MFP provides a fast and reliable technique to measure fluorescence at different wavelengths in situ, which allows discriminating between P. rubescens and other phytoplankton species. All three acoustic devices are sensitive to P. rubescens even if other scatterers, e.g., zooplankton or suspended sediment, are present in the water column, because P. rubescens containing gas vesicles has a strong density difference and hence acoustic contrast to the ambient water and other scatterers. After calibration, the combination of optical and acoustical measurements not only allows qualitative and quantitative observation of P. rubescens, but also distinction between P. rubescens, other phytoplankton, and zooplankton. As the measuring devices can sample in situ at high rates they enable assessment of plankton distributions at high temporal (minutes) and spatial (decimeters) resolution or covering large temporal (seasonal) and spatial (basin scale) scales. PMID:24303028

  8. Multi-parametric Study of Rising 3D Buoyant Flux Tubes in an Adiabatic Stratification Using AMR

    NASA Astrophysics Data System (ADS)

    Martínez-Sykora, Juan; Moreno-Insertis, Fernando; Cheung, Mark C. M.

    2015-11-01

    We study the buoyant rise of magnetic flux tubes embedded in an adiabatic stratification using two-and three-dimensional, magnetohydrodynamic simulations. We analyze the dependence of the tube evolution on the field line twist and on the curvature of the tube axis in different diffusion regimes. To be able to achieve a comparatively high spatial resolution we use the FLASH code, which has a built-in Adaptive Mesh Refinement (AMR) capability. Our 3D experiments reach Reynolds numbers that permit a reasonable comparison of the results with those of previous 2D simulations. When the experiments are run without AMR, hence with a comparatively large diffusivity, the amount of longitudinal magnetic flux retained inside the tube increases with the curvature of the tube axis. However, when a low-diffusion regime is reached by using the AMR algorithms, the magnetic twist is able to prevent the splitting of the magnetic loop into vortex tubes and the loop curvature does not play any significant role. We detect the generation of vorticity in the main body of the tube of opposite sign on the opposite sides of the apex. This is a consequence of the inhomogeneity of the azimuthal component of the field on the flux surfaces. The lift force associated with this global vorticity makes the flanks of the tube move away from their initial vertical plane in an antisymmetric fashion. The trajectories have an oscillatory motion superimposed, due to the shedding of vortex rolls to the wake, which creates a Von Karman street.

  9. Numerical analysis of the angular motion of a neutrally buoyant spheroid in shear flow at small Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Rosén, T.; Einarsson, J.; Nordmark, A.; Aidun, C. K.; Lundell, F.; Mehlig, B.

    2015-12-01

    We numerically analyze the rotation of a neutrally buoyant spheroid in a shear flow at small shear Reynolds number. Using direct numerical stability analysis of the coupled nonlinear particle-flow problem, we compute the linear stability of the log-rolling orbit at small shear Reynolds number Rea. As Rea→0 and as the box size of the system tends to infinity, we find good agreement between the numerical results and earlier analytical predictions valid to linear order in Rea for the case of an unbounded shear. The numerical stability analysis indicates that there are substantial finite-size corrections to the analytical results obtained for the unbounded system. We also compare the analytical results to results of lattice Boltzmann simulations to analyze the stability of the tumbling orbit at shear Reynolds numbers of order unity. Theory for an unbounded system at infinitesimal shear Reynolds number predicts a bifurcation of the tumbling orbit at aspect ratio λc≈0.137 below which tumbling is stable (as well as log rolling). The simulation results show a bifurcation line in the λ -Rea plane that reaches λ ≈0.1275 at the smallest shear Reynolds number (Rea=1 ) at which we could simulate with the lattice Boltzmann code, in qualitative agreement with the analytical results.

  10. Time resolved measurements of vortex-induced vibrations of a positively buoyant tethered sphere in uniform water flow

    NASA Astrophysics Data System (ADS)

    Eshbal, L.; Krakovich, A.; van Hout, R.

    2012-11-01

    Vortex-induced vibrations (VIV) of a positively buoyant (light) tethered sphere in uniform flow as well as its wake characteristics were measured in a closed loop water channel. Experiments were performed at free stream velocities ranging between 0.048 and 0.22 m/s, corresponding to sphere Reynolds numbers ranging from ReD=430 to 1925. The measurements were done using high-speed sphere tracking as well as time resolved particle image velocimetry in a horizontal plane located at the sphere's center. Until the Hopf bifurcation, the sphere remained stationary and the wake was characterized by a train of hairpin vortices exhibiting near-symmetry in the vertical plane similar to stationary sphere visualization results. For our limited parameter range, the amplitude response of two different data sets (same sphere and free stream velocity but different water viscosity) collapsed better when plotted versus ReD than when plotted versus the reduced velocity, U*. The amplitude response beyond the first bifurcation displayed continuously increasing rms amplitudes in agreement with the sphere's small mass parameter (

  11. The motion of a neutrally buoyant particle of an elliptic shape in two dimensional shear flow: A numerical study

    NASA Astrophysics Data System (ADS)

    Huang, Shih-Lin; Chen, Shih-Di; Pan, Tsorng-Whay; Chang, Chien-Cheng; Chu, Chin-Chou

    2015-08-01

    In this article, we investigate the motion of a neutrally buoyant particle of an elliptic shape freely moving in two dimensional shear flow by direct numerical simulation. An elliptic shape particle in shear flow, when initially being placed at the middle between two walls, either keeps rotating or has a stationary inclination angle depending on the particle Reynolds number R e = G r ra 2 / ν , where Gr is the shear rate, ra is the semi-long axis of the elliptic particle, and ν is the kinetic viscosity of the fluid. The critical particle Reynolds number Recr for the transition from a rotating motion to a stationary orientation depends on the aspect ratio AR = rb/ra and the confined ratio K = 2ra/H, where rb is the semi-short axis of the elliptic particle and H is the distance between two walls. Although the increasing of either parameters makes an increase in Recr, the dynamic mechanism is distinct. The AR variation causes the change of geometry shape; however, the K variation influences the wall effect. The stationary inclination angle of non-rotating slender elliptic particle with smaller confined ratio seems to depend only on the value of Re - Recr. An expected equilibrium position of the particle mass center in shear flow is the centerline between two walls. When placing the particle away from the centerline initially, it migrates either toward an equilibrium height away from the middle between two walls or back to the middle depending on the confined ratio and particle Reynolds number; but for higher particle Reynolds numbers, besides the previous two positions, the elliptic particle placed close to the middle just moves parallel to the wall with a stationary orientation.

  12. Ethyl cellulose and hydroxypropyl methyl cellulose buoyant microspheres of metoprolol succinate: Influence of pH modifiers

    PubMed Central

    Raut, Neha S; Somvanshi, Sachin; Jumde, Amol B; Khandelwal, Harsha M; Umekar, Milind J; Kotagale, Nandkishor Ramdas

    2013-01-01

    Introduction: Incorporation of pH modifier has been the usual strategy employed to enhance the dissolution of weakly basic drug from floating microspheres. Microspheres prepared using a combination of both ethyl cellulose (EC) and hydroxypropyl methylcellulose (HPMC) which shows highest release were utilize to investigate the effect of fumaric acid (FA), citric acid (CA), ascorbic acid (AA) and tartaric acid (TA) (all 5-20% w/w) incorporation on metoprolol succinate (MS) release. Materials and Methods: EC, HPMC alone or in combination were used to prepare microspheres that floated in simulated gastric fluid and evaluated for a percent yield, drug entrapment, percent buoyancy and drug release. The higher drug release in combination (MS:HPMC:EC, 1:1:2) was selected for the evaluation of influence of pH modifiers on MS release. CA (5-20% w/w), AA (5-20% w/w), FA (5-20% w/w) and TA (5-20% w/w) were added and evaluated for drug release. Present investigation is directed to develop floating drug delivery system of MS by solvent evaporation technique. Results: The microspheres of MS:HPMC:EC (1:1:2) exhibited the highest entrapment (74.36 ± 2.18). The best percentage yield was obtained at MS:HPMC (1:1) (83.96 ± 1.50) and combination of MS:HPMC:EC (1:1:2) (79.23 ± 1.63). Conclusion: MS release from the prepared microspheres was influenced by changing MS-polymer, MS-polymer-polymer ratio and pH modifier. Although significant increment in MS release was observed with CA (20% w/w), TA (20% w/w) and AA (20% w/w), addition of 20% w/w FA demonstrated more pronounced and significant increase in drug entrapment as well as release from MS:HPMC:EC (1:1:2) buoyant microspheres. PMID:24167789

  13. JBFA - buoyant flight

    NASA Technical Reports Server (NTRS)

    Ohari, T.

    1982-01-01

    A method was developed whereby a balloon was used to carry lumber out of a forest in order to continue lumber production without destroying the natural environment and view of the forest. Emphasis was on the best shape for a logging balloon, development of a balloon logging system suitable for cutting lumber and safety plans, tests on balloon construction and development of netting, and weather of mountainous areas, especially solutions to problems caused by winds.

  14. Buoyant despite Downturn

    ERIC Educational Resources Information Center

    Berry, John N., III; Fialkoff, Francine; Fox, Bette-Lee; Hadro, Josh; Horrocks, Norman; Kuzyk, Raya; Oder, Norman

    2009-01-01

    Even as libraries face the economic downturn, a record-setting number of people attended the American Library Association (ALA) annual conference in Chicago, July 9-15. The tough economy, however, was felt in the number of exhibitors, which declined from the previous record set in 2007 in Washington, DC, and in anecdotal evidence that suggested…

  15. Near-field mixing of a vertical buoyant jet in a shallow crossflow: Implications on adsorption and flocculation

    NASA Astrophysics Data System (ADS)

    Gomm, Leslie Sharon

    1999-10-01

    The behaviour and movement of pulpmill pollutants discharged into the Northern Fraser River is of significant concern due to their potential impact on this valuable aquatic ecosystem. The shallow receiving water can influence the mixing and subsequent dilution of these discharges. The association of contaminants with suspended sediment, either by direct adsorption or flocculation of contaminated solids discharged with the effluent (biosolids), also affects pollutant fate. This study examined the effects of a shallow crossflow in the near field mixing of a vertical buoyant jet, specifically dilution and trajectory. Physical mixing experiments were carried out in a shallow ambient current over a range of conditions similar to those seen in the Fraser River, specifically peak and low flow conditions. The dilution and trajectory results were then compared to those predicted by CORMIX1. The mechanism of association of contaminants with suspended sediment under these near field conditions was also investigated. A jet classification scheme was developed based on the behaviour of the jets in the shallow crossflow. Jets were classified to be Bottom, Intermediate or Surface Jets. Bottom Jets were influenced primarily by interaction of the jet with the bottom boundary layer, resulting in significantly higher levels of dilution and possible bottom attachment. The mixing of Intermediate Jets was more complicated due to interaction with both the top and bottom boundaries: the free surface inhibited mixing while interactions with the boundary layer enhanced mixing. Surface Jets were drastically affected by the free surface, with a reduction in dilution due to impingement on the free surface. The CORMIX1 model was found to be unsuitable for predicting the dilution in this application since it does not consider the effects of either the free surface or the bottom boundary layer on jet mixing. Adsorption was found to play a limited role in the near field region. Of greater

  16. Some factors affecting the use of lighter than air systems. [economic and performance estimates for dirigibles and semi-buoyant hybrid vehicles

    NASA Technical Reports Server (NTRS)

    Havill, C. D.

    1974-01-01

    The uses of lighter-than-air vehicles are examined in the present day transportation environment. Conventional dirigibles were found to indicate an undesirable economic risk due to their low speeds and to uncertainties concerning their operational use. Semi-buoyant hybrid vehicles are suggested as an alternative which does not have many of the inferior characteristics of conventional dirigibles. Economic and performance estimates for hybrid vehicles indicate that they are competitive with other transportation systems in many applications, and unique in their ability to perform some highly desirable emergency missions.

  17. 1/12-Scale mixing interface visualization and buoyant particle release tests in support of Tank 241-SY-101 hydrogen mitigation

    SciTech Connect

    Eschbach, E.J.; Enderlin, C.W.

    1993-10-01

    In support of tank waste safety programs, visualization tests were performed in the 1/12-scale tank facility, using a low-viscosity simulant. The primary objective of the tests was to obtain video records of the transient jet-sludge interaction. The intent is that these videos will provide useful qualitative data for comparison with model predictions. Two tests were initially planned: mixing interface visualization (MIV) and buoyant particle release (BPR). Completion of the buoyant particle release test was set aside in order to complete additional MIV tests. Rheological measurements were made on simulant samples before testing, and the simulant was found to exhibit thixotropic behavior. Shear vane measurements were also made on an in-situ analog of the 1/12-scale tank simulant. Simulant shear strength has been observed to be time dependent. The primary objective of obtaining video records of jet-sludge interaction was satisfied, and the records yielded jet location information which may be of use in completing model comparisons. The modeling effort is not part of this task, but this report also discusses test specific instrumentation, visualization techniques, and shear vane instrumentation which would enable improved characterization of jet-sludge interaction and simulant characteristics.

  18. HGSYSTEM/UF{sub 6} model enhancements for plume rise and dispersion around buildings, lift-off of buoyant plumes, and robustness of numerical solver

    SciTech Connect

    Hanna, S.R.; Chang, J.C.

    1997-01-01

    The HGSYSTEM/UF{sub 6} model was developed for use in preparing Safety Analysis Reports (SARs) by estimating the consequences of possible accidental releases of UF{sub 6} to the atmosphere at the gaseous diffusion plants (GDPs) located in Portsmouth, Ohio, and Paducah, Kentucky. Although the latter report carries a 1996 date, the work that is described was completed in late 1994. When that report was written, the primary release scenarios of interest were thought to be gas pipeline and liquid tank ruptures over open terrain away from the influence of buildings. However, upon further analysis of possible release scenarios, the developers of the SARs decided it was necessary to also consider accidental releases within buildings. Consequently, during the fall and winter of 1995-96, modules were added to HGSYSTEM/UF{sub 6} to account for flow and dispersion around buildings. The original HGSYSTEM/UF{sub 6} model also contained a preliminary method for accounting for the possible lift-off of ground-based buoyant plumes. An improved model and a new set of wind tunnel data for buoyant plumes trapped in building recirculation cavities have become available that appear to be useful for revising the lift-off algorithm and modifying it for use in recirculation cavities. This improved lift-off model has been incorporated in the updated modules for dispersion around buildings.

  19. The Potential for Buoyant Displacement Gas Release Events in Tank 241-SY-102 after Waste Transfer from Tank 241-SY-101

    SciTech Connect

    Wells, Beric E.; Meyer, Perry A.; Chen, Guang

    2000-04-10

    Tank 241-SY-101 is a double-shell radioactive waste storage tank containing waste that, before recent transfer and water back-dilution operations, was capable of retaining gas and producing flammable buoyant displacement gas release events (BD GREs). A BD GRE occurs when a portion of the nonconvective layer waste retains enough gas to become buoyant, rises to the waste surface, breaks up, and releases some of the stored gas. Installing the mixer pump in 1993 successfully mitigated gas retention in the settled solids layer in SY-101 and has prevented BD GREs. Gas retention in the floating drust layer and the corresponding accelerated waste level growth made it necessary to begin waste removal and back-dilution with water in December 1999. During these operations, some of the SY-101 mixed slurry layer is removed and transferred into Tank 241-SY-102. There was some concern that adding the SY-101 waste into SY-102 could create a waste configuration in SY-102 capable of BD GREs. This report updates and extends earlier assessments of the potential for BD GRE conditions in SY-102 after waste is transferred from SY-101. We determined that, under the given assumptions, no possibility of BD GREs exists in SY-102 from the SY-101 waste being added during from December 1999 through March 2000.

  20. Dynamics of the flammable plumes resulting from the convective dispersion of a fixed mass of the buoyant gaseous fuel, methane, into air.

    PubMed

    Fardisi, S; Karim, Ghazi A

    2009-08-15

    The dynamics of the dispersion of a fixed mass of the buoyant fuel, methane, when exposed with a negligible pressure difference to overlaying air within vertical cylindrical enclosures open to the atmosphere is investigated. Features of the formation and dispersion of flammable mixtures created by the gas dissipation were examined using a 3D CFD model. For the cases considered, the lean-flammable mixture boundary appears to travel mainly at a near constant rate while the rich limit front shows a more chaotic behaviour. The corresponding simulation using an axis-symmetrical 2D model tended to under-predict the dynamics of the lean and rich boundaries, for the cases considered. PMID:19237243

  1. The potential for buoyant displacement gas release events in Tank 241-SY-102 after waste transfer from Tank 241-SY-101

    SciTech Connect

    BE Wells; PE Meyer; G Chen

    2000-05-10

    Tank 241-SY-101 (SY-101) is a double-shell, radioactive waste storage tank with waste that, before the recent transfer and water back-dilution operations, was capable of retaining gas and producing buoyant displacement (BD) gas release events (GREs). Some BD GREs caused gas concentrations in the tank headspace to exceed the lower flammability limit (LFL). A BD GRE occurs when a portion of the nonconvective layer retains enough gas to become buoyant, rises to the waste surface, breaks up, and releases some of its stored gas. The installation of a mixer pump in 1993 successfully mitigated gas retention in the settled solids layer in SY-101 and has since prevented BD GREs. However, operation of the mixer pump over the years caused gas retention in the floating crust layer and a corresponding accelerated waste level growth. The accelerating crust growth trend observed in 1997--98 led to initiation of sequences of waste removal and water back-dilutions in December 1999. Waste is removed from the mixed slurry layer in Tank SY-101 and transferred into Tank 241-Sy-102 (SY-102). Water is then added back to dissolve soluble solids that retain gas. The initial transfer of 89,500 gallons of SY-101 waste, diluted in-line at 0.94:1 by volume with water, to SY-102 was conducted in December 1999. The second transfer of 230,000 gallons of original SY-101 waste, diluted approximately 0.9:1, was completed in January 2000, and the third transfer of 205,500 gallons of original SY-101 waste diluted at 0.9:1 was completed in March 2000.

  2. Modeling possible spreadings of a buoyant surface plume with lagrangian and eulerian approaches at different resolutions using flow syntheses from 1992-2007 - a Gulf of Mexico study

    NASA Astrophysics Data System (ADS)

    Tulloch, R.; Hill, C. N.; Jahn, O.

    2010-12-01

    We present results from an ensemble of BP oil spill simulations. The oil spill slick is modeled as a buoyant surface plume that is transported by ocean currents modulated, in some experiments, by surface winds. Ocean currents are taken from ECCO2 project (see http://ecco2.org ) observationally constrained state estimates spanning 1992-2007. In this work we (i) explore the role of increased resolution of ocean eddies, (ii) compare inferences from particle based, lagrangian, approaches with eulerian, field based, approaches and (ii) examine the impact of differential response of oil particles and water to normal and extreme, hurricane derived, wind stress. We focus on three main questions. Is the simulated response to an oil spill markedly different for different years, depending on ocean circulation and wind forcing? Does the simulated response depend heavily on resolution and are lagrangian and eulerian estimates comparable? We start from two regional configurations of the MIT General Circulation Model (MITgcm - see http://mitgcm.org ) at 16km and 4km resolutions respectively, both covering the Gulf of Mexico and western North Atlantic regions. The simulations are driven at open boundaries with momentum and hydrographic fields from ECCO2 observationally constrained global circulation estimates. The time dependent surface flow fields from these simulations are used to transport a dye that can optionally decay over time (approximating biological breakdown) and to transport lagrangian particles. Using these experiments we examine the robustness of conclusions regarding the fate of a buoyant slick, injected at a single point. In conclusion we discuss how future drilling operations could use similar approaches to better anticipate outcomes of accidents both in this region and elsewhere.

  3. An Experimental Field Dataset with Buoyant, Neutral, and Dense Gas Atmospheric Releases and Model Comparisons in Low-Wind Speed (Diffusion) Conditions

    SciTech Connect

    Veronica E. Wannberg, Gustavious Williams, Patrick Sawyer, and Richard Venedam

    2010-09-01

    Aunique field dataset from a series of low–wind speed experiments, modeling efforts using three commonly used models to replicate these releases, and statistical analysis of how well these models were able to predict the plume concentrations is presented. The experiment was designed to generate a dataset to describe the behavior of gaseous plumes under low-wind conditions and the ability of current, commonly used models to predict these movements. The dataset documents the release and transport of three gases: ammonia (buoyant), ethylene (neutral), and propylene (dense) in low–wind speed (diffusion) conditions. Release rates ranged from 1 to 20 kg h21. Ammonia and ethylene had five 5-min releases each to represent puff releases and five 20-min releases each to represent plume releases. Propylene had five 5-min puffs, six 20-min plumes, and a single 30-min plume. Thirty-two separate releases ranging from 6 to 47 min were conducted, of which only 30 releases generated useful data. The data collected included release rates, atmospheric concentrations to 100 m from the release point, and local meteorological conditions. The diagnostics included nine meteorological stations on 100-m centers and 36 photoionization detectors in a radial pattern. Three current stateof- the-practice models, Aerial locations of Hazardous Atmospheres (ALOHA), Emergency Prediction Information code (EPIcode), and Second-Order Closure Integrated Puff (SCIPUFF), were used to try to duplicate the measured field results. Low wind speeds are difficult to model, and all of the models had difficulty replicating the field measurements. However, the work does show that these models, if used correctly, are conservative (overpredict concentrations) and can be used for safety and emergency planning.

  4. ANALYSIS OF BUOYANT SURFACE JETS

    EPA Science Inventory

    To obtain improved prediction of heated plume characteristics from a surface jet, an integral analysis computer model was modified and a comprehensive set of field and laboratory data available from the literature was gathered, analyzed, and correlated for estimating the magnitud...

  5. Petrochronological and structural arguments for upper plate thickening and relamination of the lower plate buoyant material in the Variscan Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Peřestý, Vít; Holder, Robert; Lexa, Ondrej; Racek, Martin; Jeřábek, Petr

    2014-05-01

    Recent tectonic models for the Variscan evolution of the Bohemian Massif emphasize the role of Rayleigh-Taylor instability for the 355-340 Ma evolution of the Moldanubian domain. This model is based on the presence of weak, low-density felsic material tectonically underplating a high-density mafic layer and its subsequent gravity-driven overturn. However, earlier phases of the Variscan orogeny concerning the emplacement of felsic low-density material to the base of the upper plate are so far poorly documented. We contribute to this problem by deciphering of polyphase early-Variscan (~375 Ma) deformation and metamorphism close to the main Variscan suture. Detailed structural, pseudosection and microstructural analyses combined with LASS monazite dating were carried out in metapelites along the western margin of the upper plate represented by the Teplá Crystalline Complex (TCC). This region is represented by a ~25 km wide deformation zone with E-W metamorphic gradients associated with two distinct early-Variscan events (~380-375 and ~375-370 Ma). The first compressional event produced a vertical NNE-SSW trending fabric and a continuous and prograde Barrovian metamorphic sequence ranging from biotite to kyanite zones at a field geotherm of 20 to 25 °C/km. Subsequently, a gently SE dipping normal shear-zone associated with retrogression develops along the base of the TCC. This sub-horizontal fabric shows normal metamorphic zonation ranging from sillimanite, biotite to chlorite zones and indicates vertical shortening related to unroofing of high pressure metabasites of the underlying Mariánské-Lázně Complex. The first metamorphic fabric is interpreted to result from early thickening of the upper plate during continental underthrusting of Saxothuringian continent (380 to 375 Ma) while the second deformation and metamorphism (~370 Ma) reflects vertical shortening produced by buoyant uplift of accreted Saxothuringian felsic crust. This event is the unique yet

  6. The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites

    NASA Astrophysics Data System (ADS)

    Stefanescu, Doru M.; Moitra, Avijit; Kacar, A. Sedat; Dhindaw, Brij K.

    1990-01-01

    Directional solidification experiments in a Bridgman-type furnace were used to study particle behavior at the liquid/solid interface in aluminum metal matrix composites. Graphite or siliconcarbide particles were first dispersed in aluminum-base alloys via a mechanically stirred vortex. Then, 100-mm-diameter and 120-mm-long samples were cast in steel dies and used for directional solidification. The processing variables controlled were the direction and velocity of solidification and the temperature gradient at the interface. The material variables monitored were the interface energy, the liquid/particle density difference, the particle/liquid thermal conductivity ratio, and the volume fraction of particles. These properties were changed by selecting combinations of particles (graphite or silicon carbide) and alloys (Al-Cu, Al-Mg, Al-Ni). A model which considers process thermodynamics, process kinetics (including the role of buoyant forces), and thermophysical properties was developed. Based on solidification direction and velocity, and on materials properties, four types of behavior were predicted. Sessile drop experiments were also used to determine some of the interface energies required in calculation with the proposed model. Experimental results compared favorably with model predictions.

  7. A modeling of buoyant gas plume migration

    SciTech Connect

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

    2008-12-01

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

  8. JBFA-Buoyant Flight, Special Edition

    NASA Technical Reports Server (NTRS)

    Wada, C.; Terada, K.; Ishii, C.; Nagamatsu, K.; Makino, M.; Ichiyoshi, S.

    1982-01-01

    Progress in the project to traverse the Pacific Ocean by manned balloon is summarized. The development of a hybrid lighter than aircraft combining the buoyancy of a gas bag with the vertical lift off capabilities of the helicopter is also addressed.

  9. Simulations of Buoyant Plumes in Solar Prominences

    NASA Astrophysics Data System (ADS)

    Hurlburt, N.; Berger, T.

    2012-08-01

    Observations of solar prominences reveal a complex, dynamic flow field within them. The flow field within quiescent prominences is characterized by long "threads" and dark "bubbles" that fall and rise (respectively) in a thin sheet. The flow field in active prominences display more helical motions that travel along the axis of the prominence. We explore the possible dynamics of both of these with the aid of 2.5D MHD simulations. Our model, compressible plasma possesses density and temperature gradients and resides in magnetic field configurations that mimc those of a solar prominence. We present results of various configurations and discuss the nonlinear behavior of the resulting dynamics.

  10. Buoyant Bubbles and Cavities in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Jones, Thomas

    The latest generation of X-ray observatories has revealed a rich array of complex structures in galaxy intracluster media (ICMs). Remarkable among these discoveries is the common existence of X-ray ICM 'cavities' filled with radio synchrotron-emitting relativistic plasma. The cavities, which are generally paired and often multiple, range in size from a few kpc up to hundreds of kpc, are evidently the depositories of AGN jets. The energy contents of these 'bubbles' range above 1060 erg, making them potentially important players in ICM thermodynamics. They also carry potentially important cosmic ray and magnetic field constituents. The important problems of understanding their stability and dynamics, including how and where they share their contents are very active research topics that I will address in this talk. This work is supported by the US National Science Foundation and the University of Minnesota Supercomputing Institute.