NASA Astrophysics Data System (ADS)
Seroussi, H. L.; Rignot, E. J.; Morlighem, M.; Larour, E. Y.; Ben Dhia, H.; Aubry, D.
2010-12-01
The recent development of new higher-order, higher-resolution ice sheet models has shown that sophisticated models, such as Full-Stokes, were essential in some parts of the ice sheets, including the grounding line region. These areas are crucial for ice flow projections and can only be rigorously simulated using full 3d models. Higher-order models are well-suited to ice stream dynamics, whereas the shallow-shelf approximation is sufficient for modeling ice shelf flow. Higher-order and full-Stokes model are computationally intensive and prohibitive for large-scale modeling. There is therefore a strong need to combine such different models in order to balance computational cost and physical accuracy for the whole ice sheet. Here we present a new methodology adapted from the Arlequin framework to couple finite element shelfy-stream, higher-order and Full-Stokes models. We achieve this by strongly coupling the different approximations within the same large scale simulation. This technique is applied to the Greenland ice sheet, and compared with single-model approaches. Our new method preserves the conditioning number of the stiffness matrix, and ensures seamless stress regimes across model transition zones, hence improving numerical accuracy compared to existing techniques that use penalties or kinematical constrains. Furthermore, it optimizes the number of degrees of freedom leading to reduced computational cost. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Modeling, Analysis and Prediction (MAP) Program.
NASA Astrophysics Data System (ADS)
Montenegro-Johnson, Thomas D.; Lauga, Eric
2014-06-01
Propulsion at microscopic scales is often achieved through propagating traveling waves along hairlike organelles called flagella. Taylor's two-dimensional swimming sheet model is frequently used to provide insight into problems of flagellar propulsion. We derive numerically the large-amplitude wave form of the two-dimensional swimming sheet that yields optimum hydrodynamic efficiency: the ratio of the squared swimming speed to the rate-of-working of the sheet against the fluid. Using the boundary element method, we show that the optimal wave form is a front-back symmetric regularized cusp that is 25% more efficient than the optimal sine wave. This optimal two-dimensional shape is smooth, qualitatively different from the kinked form of Lighthill's optimal three-dimensional flagellum, not predicted by small-amplitude theory, and different from the smooth circular-arc-like shape of active elastic filaments.
Shape Optimization of Swimming Sheets
Wilkening, J.; Hosoi, A.E.
2005-03-01
The swimming behavior of a flexible sheet which moves by propagating deformation waves along its body was first studied by G. I. Taylor in 1951. In addition to being of theoretical interest, this problem serves as a useful model of the locomotion of gastropods and various micro-organisms. Although the mechanics of swimming via wave propagation has been studied extensively, relatively little work has been done to define or describe optimal swimming by this mechanism.We carry out this objective for a sheet that is separated from a rigid substrate by a thin film of viscous Newtonian fluid. Using a lubrication approximation to model the dynamics, we derive the relevant Euler-Lagrange equations to optimize swimming speed and efficiency. The optimization equations are solved numerically using two different schemes: a limited memory BFGS method that uses cubic splines to represent the wave profile, and a multi-shooting Runge-Kutta approach that uses the Levenberg-Marquardt method to vary the parameters of the equations until the constraints are satisfied. The former approach is less efficient but generalizes nicely to the non-lubrication setting. For each optimization problem we obtain a one parameter family of solutions that becomes singular in a self-similar fashion as the parameter approaches a critical value. We explore the validity of the lubrication approximation near this singular limit by monitoring higher order corrections to the zeroth order theory and by comparing the results with finite element solutions of the full Stokes equations.
Geometry of thin liquid sheet flows
NASA Technical Reports Server (NTRS)
Chubb, Donald L.; Calfo, Frederick D.; Mcconley, Marc W.; Mcmaster, Matthew S.; Afjeh, Abdollah A.
1994-01-01
Incompresible, thin sheet flows have been of research interest for many years. Those studies were mainly concerned with the stability of the flow in a surrounding gas. Squire was the first to carry out a linear, invicid stability analysis of sheet flow in air and compare the results with experiment. Dombrowski and Fraser did an experimental study of the disintegration of sheet flows using several viscous liquids. They also detected the formulation of holes in their sheet flows. Hagerty and Shea carried out an inviscid stability analysis and calculated growth rates with experimental values. They compared their calculated growth rates with experimental values. Taylor studied extensively the stability of thin liquid sheets both theoretically and experimentally. He showed that thin sheets in a vacuum are stable. Brown experimentally investigated thin liquid sheet flows as a method of application of thin films. Clark and Dumbrowski carried out second-order stability analysis for invicid sheet flows. Lin introduced viscosity into the linear stability analysis of thin sheet flows in a vacuum. Mansour and Chigier conducted an experimental study of the breakup of a sheet flow surrounded by high-speed air. Lin et al. did a linear stability analysis that included viscosity and a surrounding gas. Rangel and Sirignano carried out both a linear and nonlinear invisid stability analysis that applies for any density ratio between the sheet liquid and the surrounding gas. Now there is renewed interest in sheet flows because of their possible application as low mass radiating surfaces. The objective of this study is to investigate the fluid dynamics of sheet flows that are of interest for a space radiator system. Analytical expressions that govern the sheet geometry are compared with experimental results. Since a space radiator will operate in a vacuum, the analysis does not include any drag force on the sheet flow.
A study of thin liquid sheet flows
NASA Technical Reports Server (NTRS)
Chubb, Donald L.; Calfo, Frederick D.; Mcconley, Marc W.; Mcmaster, Matthew S.; Afjeh, Abdollah A.
1993-01-01
This study was a theoretical and experimental investigation of thin liquid sheet flows in vacuum. A sheet flow created by a narrow slit of width, W, coalesces to a point at a distance, L, as a result of surface tension forces acting at the sheet edges. As the flow coalesces, the fluid accumulates in the sheet edges. The observed triangular shape of the sheet agrees with the calculated triangular result. Experimental results for L/W as a function of Weber number, We, agree with the calculated result, L/W = the sq. root of 8We. The edge cross sectional shape is found to oscillate from elliptic to 'cigar' like to 'peanut' like and then back to elliptic in the flow direction. A theoretical one-dimensional model was developed that yielded only elliptic solutions for the edge cross section. At the points where the elliptic shapes occur, there is agreement between theory and experiment.
M. G. McKellar; J. E. O'Brien; E. A. Harvego; J. S. Herring
2007-11-01
This report presents results from the development and optimization of a reference commercialscale high-temperature electrolysis (HTE) plant for hydrogen production. The reference plant design is driven by a high-temperature helium-cooled reactor coupled to a direct Brayton power cycle. The reference design reactor power is 600 MWt, with a primary system pressure of 7.0 MPa, and reactor inlet and outlet fluid temperatures of 540° C and 900°C, respectively. The electrolysis unit used to produce hydrogen consists of 4.176 × 10 6 cells with a per-cell active area of 225 cm2. A nominal cell area-specific resistance, ASR, value of 0.4 Ohm•cm2 with a current density of 0.25 A/cm2 was used, and isothermal boundary conditions were assumed. The optimized design for the reference hydrogen production plant operates at a system pressure of 5.0 MPa, and utilizes an air-sweep system to remove the excess oxygen that is evolved on the anode side of the electrolyzer. The inlet air for the air-sweep system is compressed to the system operating pressure of 5.0 MPa in a four-stage compressor with intercooling. The overall system thermal-to-hydrogen production efficiency (based on the low heating value of the produced hydrogen) is 49.07% at a hydrogen production rate of 2.45 kg/s with the high-temperature helium-cooled reactor concept. The information presented in this report is intended to establish an optimized design for the reference nuclear-driven HTE hydrogen production plant so that parameters can be compared with other hydrogen production methods and power cycles to evaluate relative performance characteristics and plant economics.
Light-sheet optimization for microscopy
NASA Astrophysics Data System (ADS)
Wilding, Dean; Pozzi, Paolo; Soloviev, Oleg; Vdovin, Gleb; Verhaegen, Michel
2016-03-01
Aberrations, scattering and absorption degrade the performance light-sheet fluorescence microscopes (LSFM). An adaptive optics system to correct for these artefacts and to optimize the light-sheet illumination is presented. This system allows a higher axial resolution to be recovered over the field-of-view of the detection objective. It is standard selective plane illumination microscope (SPIM) configuration modified with the addition of a spatial light modulator (SLM) and a third objective for the detection of transmitted light. Optimization protocols use this transmission light allowing the extension the depth-of-field and correction of aberrations whilst retaining a thin optical section.
Stability of Thin Liquid Sheet Flows
NASA Technical Reports Server (NTRS)
McConley, Marc W.; Chubb, Donald L.; McMaster, Matthew S.; Afjeh, Abdollah A.
1997-01-01
A two-dimensional, linear stability analysis of a thin nonplanar liquid sheet flow in vacuum is carried out. A sheet flow created by a narrow slit of W and tau attains a nonplanar cross section as a consequence of cylinders forming on the sheet edge under the influence of surface tension forces. The region where these edge cylinders join the sheet is one of high curvature, and this is found to be the location where instability is most likely to occur. The sheet flow is found to be unstable, but with low growth rates for symmetric wave disturbances and high growth rates for antisymmetric disturbances. By combining the symmetric and antisymmetric disturbance modes, a wide range of stability characteristics is obtained. The product of unstable growth rate and flow time is proportional to the width-to-thickness ratio of the sift generating the sheet Three-dimensional effects can alter these results, particularly when the sheet length-to-width ratio is not much greater than unity.
Computer-Aided Light Sheet Flow Visualization
NASA Technical Reports Server (NTRS)
Stacy, Kathryn; Severance, Kurt; Childers, Brooks A.
1993-01-01
A computer-aided flow visualization process has been developed to analyze video images acquired from rotating and translating light sheet visualization systems. The computer process integrates a mathematical model for image reconstruction, advanced computer graphics concepts, and digital image processing to provide a quantitative and visual analysis capability. The image reconstruction model, based on photogrammetry, uses knowledge of the camera and light sheet locations and orientations to project two-dimensional light sheet video images into three-dimensional space. A sophisticated computer visualization package, commonly used to analyze computational fluid dynamics (CFD) data sets, was chosen to interactively display the reconstructed light sheet images, along with the numerical surface geometry for the model or aircraft under study. A description is provided of the photogrammetric reconstruction technique, and the image processing and computer graphics techniques and equipment. Results of the computer aided process applied to both a wind tunnel translating light sheet experiment and an in-flight rotating light sheet experiment are presented. The capability to compare reconstructed experimental light sheet images and CFD solutions in the same graphics environment is also demonstrated.
Primary care flow sheet for hepatitis C virus
von Aesch, Zoë; Steele, Leah S.; Shah, Hermant
2016-01-01
Abstract Objective To develop an expert-guided, evidence-based, primary care flow sheet for the monitoring of patients living with chronic untreated hepatitis C virus (HCV). Design Delphi consensus process. Setting Ontario and British Columbia. Participants Five hepatologists and 4 family physicians experienced in HCV care. Main outcome measures There were 3 rounds of consultation and revision. In round 1, participants ranked (on an 11-point scale) the importance of 27 possible clinical elements that fell under the categories of background patient information, counseling topics, and biochemical parameters; indicated the ideal frequency of such interventions (in months); and suggested additional elements. Results were collated and elements that were ranked with an average score greater than 4.9 were included in further iterations. The second and third rounds involved the circulation of draft flow sheets, and participants were asked to flag erroneous or missing elements. All comments were integrated. Results Group consensus was achieved following 3 iterations. The final flow sheet to improve monitoring of HCV in primary care includes 31 clinical elements that fall under the categories background patient information, key counseling topics, and biochemical parameters (and the intervals for such interventions). Conclusion A diverse group of experienced clinicians came to a consensus regarding optimal primary care monitoring and counseling of the untreated HCV population. Future steps include refinement and pilot-testing of this flow sheet in order to optimize its usefulness within the family medicine setting.
Plasma sheet flow damping by oscillatory flow braking
NASA Astrophysics Data System (ADS)
Panov, Evgeny V.; Leontyeva, Olga S.; Baumjohann, Wolfgang; Nakamura, Rumi; Amm, Olaf; Angelopoulos, Vassilis; Glassmeier, Karl-Heinz; Kubyshkina, Marina V.; Petrukovich, Anatoli A.; Sergeev, Victor A.; Weygand, James M.
2015-04-01
Using simultaneous observations in the near-Earth plasma sheet by five Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes, conjugate ground all-sky camera observations from Canada, and magnetometer networks over North America, we show that auroral bulge dynamics is modulated by a recently discovered process known as oscillatory flow braking, which occurs at about 10 Earth radii down the Earth's magnetotail. In oscillatory flow breaking, plasma sheet flows oscillating with different periods at various distances collide, producing pressure forces that exert shear stresses on the magnetic field, transiently amplifying the vertical magnetic field component. Sporadic fast relief of these stresses through significant particle precipitations causes damping of plasma sheet fast flows.
Emittance Measurements for a Thin Liquid Sheet Flow
NASA Technical Reports Server (NTRS)
Englehart, Amy N.; McConley, Marc W.; Chubb, Donald L.
1996-01-01
The Liquid Sheet Radiator (LSR) is an external flow radiator that uses a triangular-shaped flowing liquid sheet as the radiating surface. It has potentially much lower mass than solid wall radiators such as pumped loop and heat pipe radiators, along with being nearly immune to micrometeoroid penetration. The LSR has an added advantage of simplicity. Surface tension causes a thin (100-300 microns) liquid sheet to coalesce to a point, causing the sheet flow to have a triangular shape. Such a triangular sheet is desirable since it allows for simple collection of the flow at a single point. A major problem for all external flow radiators is the requirement that the working fluid be of very low (approx. 10(sup -8) torr) vapor pressure to keep evaporative losses low. As a result, working fluids are limited to certain oils (such as used in diffusion pumps) for low temperatures (300-400 K) and liquid metals for higher temperatures. Previous research on the LSR has been directed at understanding the fluid mechanics of thin sheet flows and assessing the stability of such flows, especially with regard to the formation of holes in the sheet. Taylor studied extensively the stability of thin liquid sheets both theoretically and experimentally. He showed that thin sheets in a vacuum are stable. The latest research has been directed at determining the emittance of thin sheet flows. The emittance was calculated from spectral transmittance data for the Dow Corning 705 silicone oil. By experimentally setting up a sheet flow, the emittance was also determined as a function of measurable quantities, most importantly, the temperature drop between the top of the sheet and the temperature at the coalescence point of the sheet. Temperature fluctuations upstream of the liquid sheet were a potential problem in the analysis and were investigated.
NASA Technical Reports Server (NTRS)
Allan, Brian; Owens, Lewis
2010-01-01
In support of the Blended-Wing-Body aircraft concept, a new flow control hybrid vane/jet design has been developed for use in a boundary-layer-ingesting (BLI) offset inlet in transonic flows. This inlet flow control is designed to minimize the engine fan-face distortion levels and the first five Fourier harmonic half amplitudes while maximizing the inlet pressure recovery. This concept represents a potentially enabling technology for quieter and more environmentally friendly transport aircraft. An optimum vane design was found by minimizing the engine fan-face distortion, DC60, and the first five Fourier harmonic half amplitudes, while maximizing the total pressure recovery. The optimal vane design was then used in a BLI inlet wind tunnel experiment at NASA Langley's 0.3-meter transonic cryogenic tunnel. The experimental results demonstrated an 80-percent decrease in DPCPavg, the reduction in the circumferential distortion levels, at an inlet mass flow rate corresponding to the middle of the operational range at the cruise condition. Even though the vanes were designed at a single inlet mass flow rate, they performed very well over the entire inlet mass flow range tested in the wind tunnel experiment with the addition of a small amount of jet flow control. While the circumferential distortion was decreased, the radial distortion on the outer rings at the aerodynamic interface plane (AIP) increased. This was a result of the large boundary layer being distributed from the bottom of the AIP in the baseline case to the outer edges of the AIP when using the vortex generator (VG) vane flow control. Experimental results, as already mentioned, showed an 80-percent reduction of DPCPavg, the circumferential distortion level at the engine fan-face. The hybrid approach leverages strengths of vane and jet flow control devices, increasing inlet performance over a broader operational range with significant reduction in mass flow requirements. Minimal distortion level requirements
Thin sheets achieve optimal wrapping of liquids
NASA Astrophysics Data System (ADS)
Paulsen, Joseph; Démery, Vincent; Davidovitch, Benny; Santangelo, Christian; Russell, Thomas; Menon, Narayanan
2015-03-01
A liquid drop can wrap itself in a sheet using capillary forces [Py et al., PRL 98, 2007]. However, the efficiency of ``capillary origami'' at covering the surface of a drop is hampered by the mechanical cost of bending the sheet. Thinner sheets deform more readily by forming small-scale wrinkles and stress-focussing patterns, but it is unclear how coverage efficiency competes with mechanical cost as thickness is decreased, and what wrapping shapes will emerge. We place a thin (~ 100 nm) polymer film on a drop whose volume is gradually decreased so that the sheet covers an increasing fraction of its surface. The sheet exhibits a complex sequence of axisymmetric and polygonal partially- and fully- wrapped shapes. Remarkably, the progression appears independent of mechanical properties. The gross shape, which neglects small-scale features, is correctly predicted by a simple geometric approach wherein the exposed area is minimized. Thus, simply using a thin enough sheet results in maximal coverage.
NASA Astrophysics Data System (ADS)
Tamasco, Cynthia M.; Rais-Rohani, Masoud; Buijk, Arjaan
2013-03-01
This article presents the development and application of a coupled finite element simulation and optimization framework that can be used for design and analysis of sheet-forming processes of varying complexity. The entire forming process from blank gripping and deep drawing to tool release and springback is modelled. The dies, holders, punch and workpiece are modelled with friction, temperature, holder force and punch speed controlled in the process simulation. Both single- and multi-stage sheet-forming processes are investigated. Process simulation is coupled with a nonlinear gradient-based optimization approach for optimizing single or multiple design objectives with imposed sheet-forming response constraints. A MATLAB program is developed and used for data-flow management between process simulation and optimization codes. Thinning, springback, damage and forming limit diagram are used to define failure in the forming process design optimization. Design sensitivity analysis and optimization results of the example problems are presented and discussed.
Evaluating the implementation of a pain management flow sheet.
Joyce, B A; Keck, J F; Gerkensmeyer, J E
1999-10-01
This study evaluated the outcome of implementing a pain flow sheet, using protocols derived from the Agency for Health Care Policy and Research (AHCPR) guidelines for pain management, for children recovering from surgery. Findings indicated the flow sheet was not used as designed; thus, implementing the flow sheet did not result in increased documentation of pain assessments, interventions, and outcomes, except in the increased documentation of nonpharmacological interventions for pain management. Rogers' Diffusion of Innovation Theory gives insight as to why this occurred and provides rationale for more intensive in-service education when new innovations are implemented. PMID:10554443
Optimal Design of Sheet Pile Wall Embedded in Clay
NASA Astrophysics Data System (ADS)
Das, Manas Ranjan; Das, Sarat Kumar
2015-09-01
Sheet pile wall is a type of flexible earth retaining structure used in waterfront offshore structures, river protection work and temporary supports in foundations and excavations. Economy is an essential part of a good engineering design and needs to be considered explicitly in obtaining an optimum section. By considering appropriate embedment depth and sheet pile section it may be possible to achieve better economy. This paper describes optimum design of both cantilever and anchored sheet pile wall penetrating clay using a simple optimization tool Microsoft Excel ® Solver. The detail methodology and its application with examples are presented for cantilever and anchored sheet piles. The effects of soil properties, depth of penetration and variation of ground water table on the optimum design are also discussed. Such a study will help professional while designing the sheet pile wall penetrating clay.
Flow-pattern evolution of the last British Ice Sheet
NASA Astrophysics Data System (ADS)
Hughes, Anna L. C.; Clark, Chris D.; Jordan, Colm J.
2014-04-01
We present a 10-stage reconstruction of the evolution in ice-flow patterns of the last British Ice Sheet from build-up to demise derived from geomorphological evidence. 100 flowsets identified in the subglacial bedform record (drumlins, mega-scale glacial lineations, and ribbed moraine) are combined with ancillary evidence (erratic-transport paths, absolute dates and a semi-independently reconstructed retreat pattern) to define flow patterns, ice divides and ice-sheet margins during build-up, maximum glaciation and retreat. Overprinting and cross-cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat. The ice-flow configuration of the last British Ice Sheet was not static. Some ice divides were remarkably stable, persisting through multiple stages of the ice-sheet evolution, whereas others were transient features existing for a short time and/or shifting in position 10s km. The 10 reconstructed stages of ice-sheet geometry capture two main modes of operation; first as an integrated ice sheet with a broadly N-S orientated ice divide, and second as a multi-domed ice sheet orientated parallel with the shelf edge. A thick integrated ice sheet developed as ice expanded out of source areas in Scotland to envelop southerly ice caps in northern England and Wales, and connect with the Irish Ice Sheet to the west and the Scandinavian Ice Sheet across the North Sea. Following break-up of ice over the North Sea, ice streaming probably drove mass loss and ice-sheet thinning to create a more complex divide structure, where ice-flow patterns were largely controlled by the form of the underlying topography. Ice surface lowering occurred before separation of, and retreat to, multiple ice centres centred over high ground. We consider this 10-stage reconstruction of the evolution in ice-sheet configuration to be the simplest palaeo
The Steady Flow Resistance of Perforated Sheet Materials in High Speed Grazing Flows
NASA Technical Reports Server (NTRS)
Syed, Asif A.; Yu, Jia; Kwan, H. W.; Chien, E.; Jones, Michael G. (Technical Monitor)
2002-01-01
A study was conducted to determine the effects of high speed grazing air flow on the acoustic resistance of perforated sheet materials used in the construction of acoustically absorptive liners placed in commercial aircraft engine nacelles. Since DC flow resistance of porous sheet materials is known to be a major component of the acoustic resistance of sound suppression liners, the DC flow resistance of a set of perforated face-sheets and linear 'wiremesh' face-sheets was measured in a flow duct apparatus (up to Mach 0.8). Samples were fabricated to cover typical variations in perforated face-sheet parameters, such as hole diameter, porosity and sheet thickness, as well as those due to different manufacturing processes. The DC flow resistance data from perforated sheets were found to correlate strongly with the grazing flow Mach number and the face-sheet porosity. The data also show correlation against the boundary layer displacement thickness to hole-diameter ratio. The increase in resistance with grazing flow for punched aluminum sheets is in good agreement with published results up to Mach 0.4, but is significantly larger than expected above Mach 0.4. Finally, the tests demonstrated that there is a significant increase in the resistance of linear 'wiremesh' type face-sheet materials.
Analysis of the flow imbalance on the profile shape during the extrusion of thin magnesium sheets
Gall, Sven; Müller, Sören; Reimers, Walter
2013-12-16
The extrusion process facilitates the production of magnesium sheets featuring a very thin thickness as well as excellent surface properties by using a single process step only. However, the extrusion of the magnesium sheets applying not optimized process parameters, e.g. low billet temperature or/ and poorly deformable magnesium alloy, produce pronounced buckling and waving of the extruded sheets as well as a variation of accuracy in profile shape along the cross section. The present investigation focuses on the FEM-simulation of the extrusion of magnesium sheets in order to clarify the origin of the mentioned effects. The simulations identify the flow imbalance during extrusion as the main critical factor. Due to the flow imbalance after passing the die a large compression stress zone is formed causing the buckling and waving of the thin sheets. Furthermore, the simulations of the magnesium sheet extrusion reveal that the interaction of the material flow gradients along the width and along the thickness direction near the die orifice lead to the variation of the accuracy in profile shape.
Systematic study of plasma flow during plasma sheet thinnings
NASA Technical Reports Server (NTRS)
Lui, A. T. Y.; Frank, L. A.; Ackerson, K. L.; Meng, C.-I.; Akasofu, S.-I.
1977-01-01
On the basis of a study of Imp 6 measurements of plasma flow, it is concluded that there is no clear indication of a predominance of tailward plasma flow beyond about X = -15 R sub E in the midnight sector of the plasma sheet during the expansive phase of a substorm. In fact, it is shown statistically that sunward plasma flow is more frequently observed in the midnight sector within about 30 R sub E from the earth than in any other direction during plasma sheet thinning at the substorm expansion. This result supports the conclusion that there is no definite evidence for the formation of a reconnection neutral line in the near-earth plasma sheet during most substorms.
The onset of chaos in vortex sheet flow
NASA Astrophysics Data System (ADS)
Krasny, Robert; Nitsche, Monika
2002-03-01
Regularized point-vortex simulations are presented for vortex sheet motion in planar and axisymmetric flow. The sheet forms a vortex pair in the planar case and a vortex ring in the axisymmetric case. Initially the sheet rolls up into a smooth spiral, but irregular small-scale features develop later in time: gaps and folds appear in the spiral core and a thin wake is shed behind the vortex ring. These features are due to the onset of chaos in the vortex sheet flow. Numerical evidence and qualitative theoretical arguments are presented to support this conclusion. Past the initial transient the flow enters a quasi-steady state in which the vortex core undergoes a small-amplitude oscillation about a steady mean. The oscillation is a time-dependent variation in the elliptic deformation of the core vorticity contours; it is nearly time-periodic, but over long times it exhibits period-doubling and transitions between rotation and nutation. A spectral analysis is performed to determine the fundamental oscillation frequency and this is used to construct a Poincaré section of the vortex sheet flow. The resulting section displays the generic features of a chaotic Hamiltonian system, resonance bands and a heteroclinic tangle, and these features are well-correlated with the irregular features in the shape of the vortex sheet. The Poincaré section also has KAM curves bounding regions of integrable dynamics in which the sheet rolls up smoothly. The chaos seen here is induced by a self-sustained oscillation in the vortex core rather than external forcing. Several well-known vortex models are cited to justify and interpret the results.
A Three-Dimensional Vortex Sheet Method for Multiphase Flows
NASA Astrophysics Data System (ADS)
Stock, Mark; Dahm, Werner; Tryggvason, Gretar
2002-11-01
Previous work on a three-dimensional vortex-in-cell method is extended to include baroclinic vorticity generation in flows with large density ratios. A vortex sheet discretization is used both to maintain the boundary between different fluids or fluid phases, and to provide for a divergence-free vorticity field at all times. Automatic insertion and deletion of triangular elements allow the vortex sheet to maintain its connectivity and resolution during the simulation, despite extensive stretching of the material surface. The VIC grid provides regularization, and the simulation is inviscid at resolved scales. Computational results for flows with weak and strong density variations are presented.
Computer-aided light sheet flow visualization using photogrammetry
NASA Technical Reports Server (NTRS)
Stacy, Kathryn; Severance, Kurt; Childers, Brooks A.
1994-01-01
A computer-aided flow visualization process has been developed to analyze video images acquired from rotating and translating light sheet visualization systems. The computer process integrates a mathematical model for image reconstruction, advanced computer graphics concepts, and digital image processing to provide a quantitative and a visual analysis capability. The image reconstruction model, based on photogrammetry, uses knowledge of the camera and light sheet locations and orientations to project two-dimensional light sheet video images into three-dimensional space. A sophisticated computer visualization package, commonly used to analyze computational fluid dynamics (CFD) results, was chosen to interactively display the reconstructed light sheet images with the numerical surface geometry for the model or aircraft under study. The photogrammetric reconstruction technique and the image processing and computer graphics techniques and equipment are described. Results of the computer-aided process applied to both a wind tunnel translating light sheet experiment and an in-flight rotating light sheet experiment are presented. The capability to compare reconstructed experimental light sheet images with CFD solutions in the same graphics environment is also demonstrated.
Application of Six Sigma Robust Optimization in Sheet Metal Forming
Li, Y.Q.; Cui, Z.S.; Ruan, X.Y.; Zhang, D.J.
2005-08-05
Numerical simulation technology and optimization method have been applied in sheet metal forming process to improve design quality and shorten design cycle. While the existence of fluctuation in design variables or operation condition has great influence on the quality. In addition to that, iterative solution in numerical simulation and optimization usually take huge computational time or endure expensive experiment cost In order to eliminate effect of perturbations in design and improve design efficiency, a CAE-based six sigma robust design method is developed in this paper. In the six sigma procedure for sheet metal forming, statistical technology and dual response surface approximate model as well as algorithm of 'Design for Six Sigma (DFSS)' are integrated together to perform reliability optimization and robust improvement. A deep drawing process of a rectangular cup is taken as an example to illustrate the method. The optimization solutions show that the proposed optimization procedure not only improves significantly the reliability and robustness of the forming quality, but also increases optimization efficiency with approximate model.
Spatial complexity of ice flow across the Antarctic Ice Sheet
NASA Astrophysics Data System (ADS)
Ng, Felix S. L.
2015-11-01
Fast-flowing ice streams carry ice from the interior of the Antarctic Ice Sheet towards the coast. Understanding how ice-stream tributaries operate and how networks of them evolve is essential for developing reliable models of the ice sheet’s response to climate change. A particular challenge is to unravel the spatial complexity of flow within and across tributary networks. Here I define a measure of planimetric flow convergence, which can be calculated from satellite measurements of the ice sheet’s surface velocity, to explore this complexity. The convergence map of Antarctica clarifies how tributaries draw ice from its interior. The map also reveals curvilinear zones of convergence along lateral shear margins of streaming, and abundant ripples associated with nonlinear ice rheology and changes in bed topography and friction. Convergence on ice-stream tributaries and their feeding zones is uneven and interspersed with divergence. For individual drainage basins, as well as the ice sheet as a whole, fast flow cannot converge or diverge as much as slow flow. I therefore deduce that flow in the ice-stream networks is subject to mechanical regulation that limits flow-orthonormal strain rates. These findings provide targets for ice-sheet simulations and motivate more research into the origin and dynamics of tributarization.
Flow of Magnetohydrodynamic Micropolar Fluid Induced by Radially Stretching Sheets
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Nawaz, Muhammad; Hendi, Awatif A.
2011-02-01
We investigate the flow of a micropolar fluid between radial stretching sheets. The magnetohydrodynamic (MHD) nonlinear problem is treated using the homotopy analysis method (HAM) and the velocity profiles are predicted for the pertinent parameters. The values of skin friction and couple shear stress coefficients are obtained for various values of Reynolds number, Hartman number, and micropolar fluid parameter.
33. Photograph of a line drawing. 'EQUIPMENT FLOW SHEET, BUILDING ...
33. Photograph of a line drawing. 'EQUIPMENT FLOW SHEET, BUILDING 'D', PLANT 'B'. Holston Ordnance Works, Tennessee Eastman Corporation. August 4, 1942. Delineator: Hattaway. Drawing # 7651-1004.218. - Holston Army Ammunition Plant, RDX-and-Composition-B Manufacturing Line 9, Kingsport, Sullivan County, TN
Laminar Entrained Flow Reactor (Fact Sheet)
Not Available
2014-02-01
The Laminar Entrained Flow Reactor (LEFR) is a modular, lab scale, single-user reactor for the study of catalytic fast pyrolysis (CFP). This system can be employed to study a variety of reactor conditions for both in situ and ex situ CFP.
NASA Astrophysics Data System (ADS)
Lyons, L. R.; Nishimura, Y.; Gallardo-Lacourt, B.; Nicolls, M. J.; Chen, S.; Hampton, D. L.; Bristow, W. A.; Ruohoniemi, J. M.; Nishitani, N.; Donovan, E. F.; Angelopoulos, V.
2015-06-01
We have combined radar observations and auroral images obtained during the Poker Flat Incoherent Scatter Radar Ion Neutral Observations in the Thermosphere campaign to show the common occurrence of westward moving, localized auroral brightenings near the auroral equatorward boundary and to show their association with azimuthally moving flow bursts near or within the subauroral polarization stream (SAPS) region. These results indicate that the SAPS region, rather than consisting of relatively stable proton precipitation and westward flows, can have rapidly varying flows, with speeds varying from ~100 m/s to ~1 km/s in just a few minutes. The auroral brightenings are associated with bursts of weak electron precipitation that move westward with the westward flow bursts and extend into the SAPS region. Additionally, our observations show evidence that the azimuthally moving flow bursts often connect to earthward (equatorward in the ionosphere) plasma sheet flow bursts. This indicates that rather than stopping or bouncing, some flow bursts turn azimuthally after reaching the inner plasma sheet and lead to the bursts of strong azimuthal flow. Evidence is also seen for a general guiding of the flow bursts by the large-scale convection pattern, flow bursts within the duskside convection being azimuthally turned to the west, and those within the dawn cell being turned toward the east. The possibility that the SAPS region flow structures considered here may be connected to localized flow enhancements from the polar cap that cross the nightside auroral poleward boundary and lead to flow bursts within the plasma sheet warrants further consideration.
Interpretation of high-speed flows in the plasma sheet
NASA Technical Reports Server (NTRS)
Chen, C. X.; Wolf, R. A.
1993-01-01
Pursuing an idea suggested by Pontius and Wolf (1990), we propose that the `bursty bulk flows' observed by Baumjohann et al. (1990) and Angelopoulos et al. (1992) are `bubbles' in the Earth's plasma sheet. Specifically, they are flux tubes that have lower values of pV(exp 5/3) than their neighbors, where p is the thermal pressure of the particles and V is the volume of a tube containing one unit of magnetic flux. Whether they are created by reconnection or some other mechanism, the bubbles are propelled earthward by a magnetic buoyancy force, which is related to the interchange instability. Most of the major observed characteristics of the bursty bulk flows can be interpreted naturally in terms of the bubble picture. We propose a new `stratified fluid' picture of the plasma sheet, based on the idea that bubbles constitute the crucial transport mechanism. Results from simple mathematical models of plasma sheet transport support the idea that bubbles can resolve the pressure balance inconsistency, particularly in cases where plasma sheet ions are lost by gradient/curvature drift out the sides of the tail or bubbles are generated by reconnection in the middle of plasma sheet.
Optimal energy growth in swept Hiemenz flow
NASA Astrophysics Data System (ADS)
Guegan, Alan; Huerre, Patrick; Schmid, Peter
2006-11-01
It has been shown in Gu'egan, Schmid & Huerre 2006 that the kinetic energy of optimal G"ortler-H"ammerlin (GH) perturbations in swept Hiemenz flow can be transiently amplified by two orders of magnitude at Reynolds numbers ranging from 400 to 1000 and spanwise wavenumbers from 0.1 to 0.5. In this configuration an array of counter-rotating chordwise vortices is compressed by the spanwise shear, as in the well-known Orr mechanism. We show that stronger transient growth can be achieved when the GH assumption is relaxed. In this case the optimal initial perturbation consists in vorticity sheets stacked in the chordwise direction, at a small angle from the symmetry plane of the base flow. Although the spatial structure of the GH perturbations is lost, wall-normal-spanwise plane cuts show that the amplification mechanism is mostly unchanged. The GH assumption thus provides a reasonably good estimate for transient energy amplification levels in swept Hiemenz flow. Extension of this analysis to the spatial growth problem is under way and preliminary results will be shown.
Modelling water flow under glaciers and ice sheets
Flowers, Gwenn E.
2015-01-01
Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082
Non-Linear Optical Flow Cytometry Using a Scanned, Bessel Beam Light-Sheet
Collier, Bradley B.; Awasthi, Samir; Lieu, Deborah K.; Chan, James W.
2015-01-01
Modern flow cytometry instruments have become vital tools for high-throughput analysis of single cells. However, as issues with the cellular labeling techniques often used in flow cytometry have become more of a concern, the development of label-free modalities for cellular analysis is increasingly desired. Non-linear optical phenomena (NLO) are of growing interest for label-free analysis because of the ability to measure the intrinsic optical response of biomolecules found in cells. We demonstrate that a light-sheet consisting of a scanned Bessel beam is an optimal excitation geometry for efficiently generating NLO signals in a microfluidic environment. The balance of photon density and cross-sectional area provided by the light-sheet allowed significantly larger two-photon fluorescence intensities to be measured in a model polystyrene microparticle system compared to measurements made using other excitation focal geometries, including a relaxed Gaussian excitation beam often used in conventional flow cytometers. PMID:26021750
Non-linear optical flow cytometry using a scanned, Bessel beam light-sheet.
Collier, Bradley B; Awasthi, Samir; Lieu, Deborah K; Chan, James W
2015-01-01
Modern flow cytometry instruments have become vital tools for high-throughput analysis of single cells. However, as issues with the cellular labeling techniques often used in flow cytometry have become more of a concern, the development of label-free modalities for cellular analysis is increasingly desired. Non-linear optical phenomena (NLO) are of growing interest for label-free analysis because of the ability to measure the intrinsic optical response of biomolecules found in cells. We demonstrate that a light-sheet consisting of a scanned Bessel beam is an optimal excitation geometry for efficiently generating NLO signals in a microfluidic environment. The balance of photon density and cross-sectional area provided by the light-sheet allowed significantly larger two-photon fluorescence intensities to be measured in a model polystyrene microparticle system compared to measurements made using other excitation focal geometries, including a relaxed Gaussian excitation beam often used in conventional flow cytometers. PMID:26021750
Hon, K.; Kauahikaua, J.; Denlinger, R.; Mackay, K.
1994-01-01
Inflated pahoehoe sheet flows have a distinctive horizontal upper surface, which can be several hundred meters across, and are bounded to steep monoclinal uplifts. The inflated sheet flows studied ranged from 1 to 5 m in thickness, but initially propagated as thin sheets of fluid pahoehoe lava, generally 20-30 cm thick. The morphology of the lava as flow advanced is described. Inflated sheet flows from Kilauea and Mauna Loa are morphologically similar to some thick Icelandic and submarine sheet flows, suggesting a similar mechanism of emplacement. -from Authors
How does ice sheet loading affect ocean flow around Antarctica?
NASA Astrophysics Data System (ADS)
Dijkstra, H. A.; Rugenstein, M. A.; Stocchi, P.; von der Heydt, A. S.
2012-12-01
Interactions and dynamical feedbacks between ocean circulation, heat and atmospheric moisture transport, ice sheet evolution, and Glacial Isostatic Adjustment (GIA) are overlooked issues in paleoclimatology. Here we will present first results on how ocean flows were possibly affected by the glaciation of Antarctica across the Eocene-Oligocene Transition (~ 34 Ma) through GIA and bathymetry variations. GIA-induced gravitationally self-consistent bathymetry variations are determined by solving the Sea Level Equation (SLE), which describes the time dependent shape of (i) the solid Earth and (ii) the equipotential surface of gravity. Since the ocean circulation equations are defined relative to the equipotential surface of gravity, only bathymetry variations can influence ocean flows, although the sea surface slope will also change through time due to gravitational attraction. We use the Hallberg Isopycnal Model under late Eocene conditions to calculate equilibrium ocean flows in a domain in which the bathymetry evolves under ice loading according to the SLE. The bathymetric effects of the glaciation of Antarctica lead to substantial spatial changes in ocean flows, and close to the coast, the flow even reverses direction. Volume transports through the Drake Passage and Tasman Seaway adjust to the new bathymetry. The results indicate that GIA-induced ocean flow variations alone may have had an impact on sedimentation and erosion patterns, the repositioning of fronts, ocean heat transport and grounding line and ice sheet stability.
Earthward and tailward flows in the plasma sheet
NASA Astrophysics Data System (ADS)
Zhang, L. Q.; Wang, J. Y.; Baumjohann, W.; Rème, H.; Dunlop, M. W.
2015-06-01
Utilizing C3/Cluster satellite observations from the year of 2001 to 2006, we investigated the earthward flow (EF) and tailward flow (TF) at Bz > 0 in the plasma sheet. We found that the EF and the TF have similar spatial distributions. Both characteristics are independent of the distance beyond 14 RE. Both flows are deflected while closer to the Earth. Statistical results further showed that the EF/TF occur in the central plasma sheet as well as the plasma sheet boundary layer and can be observed during quiet times and periods of geomagnetic activity. A typical event reveals that the EF and the TF have different plasma population. A transition region (TR) can be formed at the interface between the EF and TF. Very significant duskward components appeared in bulk velocities for both populations. It appears that the vortical-like structure can be formed near the TR. The magnetic field within the TR is twisted and strongly fluctuates. No clear magnetic flux pileups are observed inside the TR.
Analyzing low frequency waves associated with plasma sheet flow channels
NASA Astrophysics Data System (ADS)
Xing, X.; Liang, J.; Wang, C. P.; Lyons, L. R.; Angelopoulos, V.
2014-12-01
Low frequency (0.006~0.02 Hz) magnetic oscillations are frequently observed to be associated with the substorm-related dipolarization in the near-Earth plasma sheet. It has been suggested that these oscillations are possibly triggered by ballooning instability in the transition region. However, our multi-point observations using THEMIS spacecraft have shown that similar oscillations are observed to be associated with the earthward moving flow channels as they penetrate from middle tail to the transition region. Linear MHD wave analysis suggested that these oscillations ahead of the dipolarization front are magnetosonic waves. For most of the cases, the thermal pressure and magnetic pressures variations are anti-phase, indicating slow mode waves. However, by taking advantage of the spacecraft located very close in X-Y plane and slightly away from the central plasma sheet, we found that for many events the phase relation between the thermal and magnetic pressure variations is Z-dependent, which suggests that the observational evidence for slow mode may not be applicable. In order to further examine these waves, we performed a MHD analysis in inhomogeneous plasma sheet. The calculation shows that for Harris Sheet configuration, the thermal and magnetic pressures variations can be anti-phase for any wave other than slow mode waves where the vertical velocity disturbance reaches its maximum, thus this phase relation may not be used as an identifier of magnetosonic wave modes. We will show the dispersion relation and wave generated disturbances obtained from the numerical calculations.
Bayesian Inversion for Large Scale Antarctic Ice Sheet Flow
NASA Astrophysics Data System (ADS)
Ghattas, O.; Isaac, T.; Petra, N.; Stadler, G.
2014-12-01
The flow of ice from the interior of polar ice sheets is the primarycontributor to projected sea level rise. One of the main difficultiesfaced in modeling ice sheet flow is the uncertain spatially-varyingRobin boundary condition that describes the resistance to sliding atthe base of the ice. Satellite observations of the surface ice flowvelocity, along with a model of ice as a creeping incompressibleshear-thinning fluid, can be used to infer this uncertain basalboundary condition. We cast this ill-posed inverse problem in theframework of Bayesian inference, which allows us to infer not only thebasal sliding parameters, but also the associated uncertainty. Toovercome the prohibitive nature of Bayesian methods for large-scaleinverse problems, we exploit the fact that, despite the large size ofobservational data, they typically provide only sparse information onmodel parameters. We show results for Bayesian inversion of the basalsliding parameter field for the full Antarctic continent, anddemonstrate that the work required to solve the inverse problem,measured in number of forward (and adjoint) ice sheet model solves, isindependent of the parameter dimension, data dimension, and number ofprocessor cores.
Optimization of Forming Processes with Different Sheet Metal Alloys
NASA Astrophysics Data System (ADS)
Sousa, Luísa C.; Castro, Catarina F.; António, Carlos C.
2007-05-01
Over the past decades relatively heavy components made of steel alloys comprise the majority of many manufactured parts due to steel's low cost, high formability and good strength. The desire to produce lightweight parts has led to studies searching for lighter and stronger materials such as aluminum alloys. However, they exhibit lower elastic stiffness than steel resulting in higher elastic strains causing known distortions such as spring-back and so decreasing accuracy of manufactured net-shape components. This paper presents a developed computational method to optimize the design of sheet metal processes using genetic algorithms. An inverse approach is considered so that the final geometry of the bended blank closely follows a prescribed one. The developed computational method couples a finite element forming simulation and an evolutionary algorithm searching the optimal design parameters of the process. The developed method searches the optimal parameters that ensure a perfect net-shape part. Different aluminum alloys candidates for automotive structural applications are considered and the optimal solutions are analyzed.
Visualization of diffuser outlet flow using liquid crystal sheets
Kirkpatrick, A.T.
1995-08-01
This article describes a new imaging technique to determine air temperatures and flow fields from HVAC diffusers. The technique uses liquid crystal sheets to record the airflow and temperatures in color. The air temperature field is an important contributor to the thermal comfort in a room and is used to evaluate diffuser performance. Visualization of the temperature field allows one to see directly the flow field and how it is interacting with the room air. a particular application is to cold-air distribution systems that supply cooling and ventilation air to rooms at temperatures lower than in conventional systems. In these systems the cold-air supply is as low as 39 F (4 C), instead of the conventional value of 55 F (13 C). This new technique uses a temperature-sensitive liquid crystal sheet to create a visual measuring tool. The liquid crystals are layered on a plane sheet and produce two-dimensional color images of the air temperature field. Since air is invisible, some type of indicator placed in the air stream is required to determine the air temperature. At present, instruments such as thermocouples and thermistors determine the air temperature in rooms and measure the value at a single point. Information about the temperature and flow field in a room is obtained by moving the device, or using multiple sensors. This is a time-consuming process, and only yields information at the points of measurement. However, the temperature field is usually unsteady, due to variable air currents and cooling loads, so a movable device is not entirely suitable, and multiple instruments require multiple data acquisition channels. It would be more informative to visualize the entire airflow from the diffuser at any instant. This article deals with a temperature characterization method.
Sheet Flows, Avalanches, and Dune Evolution on Earth and Mars
NASA Technical Reports Server (NTRS)
2003-01-01
This investigation is a collaboration between researchers at Cornell University, the University of Florida, and the University of Rennes 1, France. Flow modeling at Cornell University focused on mechanisms for the suspension and transport of wind-blown sand that are important in both terrestrial and Martian environments. These mechanisms include the saltation (or jumping) of grains, collisions between grains, and the interaction of grains with the velocity fluctuations of the turbulent wind. Of particular interest are sheet flows; these are relatively thin, highly concentrated regions of grains flowing near the ground under the influence of a strong turbulent wind. In them, the grains are suspended by interparticle collisions. Sheet flows may be relatively rare events, but they have the capacity to move great amounts of sand. In order to describe sheet flows, a turbulent mixture theory was formulated for particles in a fluid in which fluctuations in the volume fiaction of the particles take place on the scale of the turbulent eddies. Ensemble averaged equations for particle and fluid mass, momentum, and energy and fluid rate of dissipation were expressed in terms of Farve (concentration) averaged velocities and the associated velocity fluctuations. Correlations that describe the turbulent suspension of particles and dissipation of turbulent energy of both phases due to fluid particle interactions were modeled and boundary conditions at the bed and at the upper surface of the collisional flow were formulated. The boundary conditions at the upper surface were tested in a numerical simulation developed at the University of Florida. Steady and unsteady solutions for steady and unsteady fully-developed flows were obtained over a range of wind speeds fiom the lowest for which collisional between particles occurred to at which turbulent suspension is found to dominate collisional suspension. Below the value of the wind speed at which collisions between particles were
Neptunium flow-sheet verification at reprocessing plants
Rance, P.; Chesnay, B.; Killeen, T.; Murray, M.; Nikkinen, M.; Petoe, A.; Plumb, J.; Saukkonen, H.
2007-07-01
Due to their fissile nature, neptunium and americium have at least a theoretical potential application as nuclear explosives and their proliferation potential was considered by the IAEA in studies in the late 1990's. This work was motivated by an increased awareness of the proliferation potential of americium and neptunium and a number of emerging projects in peaceful nuclear programmes which could result in an increase in the available quantities of these minor actinides. The studies culminated in proposals for various voluntary measures including the reporting of international transfers of separated americium and neptunium, declarations concerning the amount of separated neptunium and americium held by states and the application of flow-sheet verification to ensure that facilities capable of separating americium or neptunium are operated in a manner consistent with that declared. This paper discusses the issue of neptunium flowsheet verification in reprocessing plants. The proliferation potential of neptunium is first briefly discussed and then the chemistry of neptunium relevant to reprocessing plants described with a view to indicating a number of issues relevant to the verification of neptunium flow-sheets. Finally, the scope of verification activities is discussed including analysis of process and engineering design information, plant monitoring and sampling and the potential application of containment and surveillance measures. (authors)
Bursty bulk flows in the inner central plasma sheet
NASA Technical Reports Server (NTRS)
Angelopoulos, V.; Baumjohann, W.; Kennel, C. F.; Coronti, F. V.; Kivelson, M. G.; Pellat, R.; Walker, R. J.; Luehr, H.; Paschmann, G.
1992-01-01
High-speed flows in the inner central plasma sheet (first reported by Baumjohann et al. (1990) are studied, together with the concurrent behavior of the plasma and magnetic field, by using AMPTE/IRM data from about 9 to 19 R(E) in the earth magnetotail. The conclusions drawn from the detailed analysis of a representative event are reinforced by a superposed epoch analysis applied on two years of data. The high-speed flows organize themselves in 10-min time scale flow enhancements called here bursty-bulk flow (BBF) events. Both temporal and spatial effects are responsible for their bursty nature. The flow velocity exhibits peaks of very large amplitude with a characteristic time scale of the order of a minute, which are usually associated with magnetic field dipolarizations and ion temeperature increases. The BBFs represent intervals of enhanced earthward convection and energy transport per unit area in the y-z GSM direction of the order of 5 x 10 exp 19 ergs/R(E-squared).
Optimization of solver for gas flow modeling
NASA Astrophysics Data System (ADS)
Savichkin, D.; Dodulad, O.; Kloss, Yu
2014-05-01
The main purpose of the work is optimization of the solver for rarefied gas flow modeling based on the Boltzmann equation. Optimization method is based on SIMD extensions for ×86 processors. Computational code is profiled and manually optimized with SSE instructions. Heat flow, shock waves and Knudsen pump are modeled with optimized solver. Dependencies of computational time from mesh sizes and CPU capabilities are provided.
Development of a novel carrier optimized for cell sheet transplantation.
Amagai, Yosuke; Karasawa, Kaoru; Kyungsook, Jung; Matsuda, Akira; Kojima, Masanori; Watanabe, Jun; Hibi, Toyoji; Matsuda, Hiroshi; Tanaka, Akane
2015-01-01
Tissue engineering is a rapidly advancing technology in the field of regenerative medicine. For the transplantation of cell sheets, a carrier must maintain the shape of a cell sheet from a culture dish to affected sites as well as release the sheet easily onto the lesion. In this study, we examined the utility of a novel, poly(lactic acid)-based carrier for cell sheets transplantation to the cornea of dogs and the skin of rats. The poly(lactic acid)-based carrier easily picked a cell sheet up from the dish, fit to the shape of the transplantation sites, and saved time for cell sheets detachment comparing to a conventional carrier. Thus, the poly(lactic acid)-based carrier would be useful for easy cell sheet transplantations. PMID:25869322
The Optimal Configuration of Gel Sheet Governed by its Concentration
NASA Astrophysics Data System (ADS)
Zhai, Xiaobo; Zhang, Shengli; Zhang, Lei; Zhao, Shumin
2012-07-01
We investigate the configuration of gel sheets with centrosymmetric distribution of monomer concentration in this paper. The configuration energy of these gel sheets consists of the in-plane stretching energy and bending energy. The equilibrium shape equations are derived by variation principle. This provides a way to control the shape of gel sheets by the initial concentration and thickness. From the equilibrium shape equations, we know that the Gaussian curvature on boundary (K|C) of equilibrium shape is determined by the Poisson ratio hat {ν }. K|C is negative when hat {ν }>0 but positive when hat {ν }<0. Specially, we derive two dome-like solutions from the equilibrium shape equations to compare with the experimental data. In these dome-like sheets, on the boundary part the Gaussian curvature is K < 0, which is different from the center part (K > 0). Furthermore, we deduce that the initial gel distribution of cylinder sheets is proportional to 1/r and find that N-isopropylacrylamide cylinder sheets cannot be formed without additional edges. Our theoretical results agree well with the experimental data [Klein et al., Science 315, 1116 (2007)]. On the other hand, we predict a special type of gel sheets as minimal surface. Their residual stresses are constant and same along radial and circumference directions. For axisymmetric sheets, we give a criterion about the sign of Gaussian curvature K when thickness h is infinite small.
Traffic Flow Management and Optimization
NASA Technical Reports Server (NTRS)
Rios, Joseph Lucio
2014-01-01
This talk will present an overview of Traffic Flow Management (TFM) research at NASA Ames Research Center. Dr. Rios will focus on his work developing a large-scale, parallel approach to solving traffic flow management problems in the national airspace. In support of this talk, Dr. Rios will provide some background on operational aspects of TFM as well a discussion of some of the tools needed to perform such work including a high-fidelity airspace simulator. Current, on-going research related to TFM data services in the national airspace system and general aviation will also be presented.
Evaluation and optimization of silicon sheet solar cells
NASA Technical Reports Server (NTRS)
Yoo, H.; Iles, P.; Tanner, D.; Pollock, G.; Uno, F.
1980-01-01
This paper describes the results and procedures to evaluate and improve the efficiency of solar cells made from various unconventional silicon sheets. The performance parameters included photovoltaic characteristics, spectral response, dark I-V characteristics, and diffusion length. The evaluation techniques used provided accurate and reliable information on sheet performance, and self-consistent results were obtained from the various measurement techniques used. Minority carrier diffusion length (L) was shown to be the ultimate limiting factor for the sheet cell performance (efficiency) and other back-up measurements confirmed this L-dependence. Limited efforts were made to identify defects which influence cell performance, and to use some improved process methods to increase cell efficiency.
Optimal flow for brown trout: Habitat - prey optimization.
Fornaroli, Riccardo; Cabrini, Riccardo; Sartori, Laura; Marazzi, Francesca; Canobbio, Sergio; Mezzanotte, Valeria
2016-10-01
The correct definition of ecosystem needs is essential in order to guide policy and management strategies to optimize the increasing use of freshwater by human activities. Commonly, the assessment of the optimal or minimum flow rates needed to preserve ecosystem functionality has been done by habitat-based models that define a relationship between in-stream flow and habitat availability for various species of fish. We propose a new approach for the identification of optimal flows using the limiting factor approach and the evaluation of basic ecological relationships, considering the appropriate spatial scale for different organisms. We developed density-environment relationships for three different life stages of brown trout that show the limiting effects of hydromorphological variables at habitat scale. In our analyses, we found that the factors limiting the densities of trout were water velocity, substrate characteristics and refugia availability. For all the life stages, the selected models considered simultaneously two variables and implied that higher velocities provided a less suitable habitat, regardless of other physical characteristics and with different patterns. We used these relationships within habitat based models in order to select a range of flows that preserve most of the physical habitat for all the life stages. We also estimated the effect of varying discharge flows on macroinvertebrate biomass and used the obtained results to identify an optimal flow maximizing habitat and prey availability. PMID:27320735
Optimization of the excitation light sheet in selective plane illumination microscopy.
Gao, Liang
2015-03-01
Selective plane illumination microscopy (SPIM) allows rapid 3D live fluorescence imaging on biological specimens with high 3D spatial resolution, good optical sectioning capability and minimal photobleaching and phototoxic effect. SPIM gains its advantage by confining the excitation light near the detection focal plane, and its performance is determined by the ability to create a thin, large and uniform excitation light sheet. Several methods have been developed to create such an excitation light sheet for SPIM. However, each method has its own strengths and weaknesses, and tradeoffs must be made among different aspects in SPIM imaging. In this work, we present a strategy to select the excitation light sheet among the latest SPIM techniques, and to optimize its geometry based on spatial resolution, field of view, optical sectioning capability, and the sample to be imaged. Besides the light sheets discussed in this work, the proposed strategy is also applicable to estimate the SPIM performance using other excitation light sheets. PMID:25798312
The flow over bedload sheets and sorted bedforms
NASA Astrophysics Data System (ADS)
Blondeaux, Paolo; Vittori, Giovanna
2014-08-01
Field surveys show the existence of morphological patterns (named bed load sheets in fluvial enviroments and sorted bedforms in coastal environments) which consist of alternate bands of coarse and fine sediments and are characterized by a negligible spatial variation of the bottom elevation. Previous analyses show that these bottom patterns are self-organizing features which are originated by the interaction of poorly sorted sediments, fractional sediment transport and turbulence dynamics. Presently, we describe the results of an investigation of turbulence dynamics over a flat bottom but characterized by alternate bands of small and large roughness. Turbulence characteristics are obtained by means of the two-equation turbulence model of Saffman (1970) which is shown to provide a reliable description of turbulence structure both in steady and oscillatory flows, as those generated in coastal environments by surface wave propagation. Moreover, the turbulence model can describe both smooth and rough walls and provide fair results also at moderate values of the Reynolds number. The results are validated by comparing the predictions of the model with the experimental data of Jensen et al. (1989) and Fredsøe et al. (1993) who measured the velocity field and the bottom shear stress under a turbulent oscillatory flow over a plane bed with a uniform roughness and sudden spatial change of the roughness size, respectively. The measurements of Fredsøe et al. (1993) were simulated also by Fuhrman et al. (2011) by means of the k-ω turbulence model of Wilcox (2006, 2008) and an indirect comparison of the model results with the results of Fuhrman et al. (2011) can be made. The investigation shows that the streamwise advection of turbulence plays a significant role such that turbulence is more intense over the rough bottom than over the smooth bottom, if a region close to the bottom is considered. However, moving far from the bottom, an opposite trend is found. Moreover, the
NASA Astrophysics Data System (ADS)
Greenwood, Sarah L.; Clark, Chris D.
2009-12-01
The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one 'flowsets' comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset cross-cutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative 'age-stack' of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset - its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, 'smudged' landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories
Continuously Optimized Reliable Energy (CORE) Microgrid: Models & Tools (Fact Sheet)
Not Available
2013-07-01
This brochure describes Continuously Optimized Reliable Energy (CORE), a trademarked process NREL employs to produce conceptual microgrid designs. This systems-based process enables designs to be optimized for economic value, energy surety, and sustainability. Capabilities NREL offers in support of microgrid design are explained.
A synchronous strobed laser light sheet for helicopter model rotor flow visualization
NASA Technical Reports Server (NTRS)
Leighty, Bradley D.; Rhodes, David B.; Jones, Stephen B.; Franke, John M.
1990-01-01
A synchronous, strobed laser light sheet has been developed for use in flow visualization of a helicopter rotor model. The light sheet strobe circuit included selectable blade position, strobe duration, and multiple pulses per revolution for rotors having 2 to 9 blades. The flow was seeded with propylene glycol. Between runs, a calibration grid board was placed in the plane of the laser sheet and recorded with the video camera at the position used to record the flow field. A slip-sync mode permitted slow motion visualization of the flow field over complete rotations of the rotor. The system was used to make two-dimensional flow field cuts of a four-bladed rotor operating at advance ratio of 0.37 at wind tunnel speeds up to 79.25 meters per second (260 feet per second).
Separation of sheet flow on the surface of a circular cylinder
NASA Astrophysics Data System (ADS)
Isshiki, Hiroshi; Yoon, Bum-Sang; Yum, Deuk-Joon
2009-08-01
The shape of a spout of a pot is very important for the liquid to flow smoothly from the pot. This is known as the "teapot effect." Separation of flow must take place at the tip of the spout. Separation of sheet flow on the surface of a circular cylinder may provide an explanation as to why pot spouts have such a unique shape. As can be easily observed by a simple experiment, separation of sheet flow from the surface of a circular cylinder is a very interesting phenomenon beyond intuition. In the nonviscous case, the flow released at the top of the surface may proceed completely around the surface and come back to the flow start point without separation. In the present paper, effects of gravity and viscosity on sheet flow are theoretically explained and the theory is verified by experiments. The results of the theoretical model proposed in the present study were very similar to the experimental measurements. In the present study, the effects of viscosity on sheet flow on a circular cylinder, the location of flow separation, and other associated responses were investigated.
Fu, Qinyi; Martin, Benjamin L.; Matus, David Q.; Gao, Liang
2016-01-01
Despite the progress made in selective plane illumination microscopy, high-resolution 3D live imaging of multicellular specimens remains challenging. Tiling light-sheet selective plane illumination microscopy (TLS-SPIM) with real-time light-sheet optimization was developed to respond to the challenge. It improves the 3D imaging ability of SPIM in resolving complex structures and optimizes SPIM live imaging performance by using a real-time adjustable tiling light sheet and creating a flexible compromise between spatial and temporal resolution. We demonstrate the 3D live imaging ability of TLS-SPIM by imaging cellular and subcellular behaviours in live C. elegans and zebrafish embryos, and show how TLS-SPIM can facilitate cell biology research in multicellular specimens by studying left-right symmetry breaking behaviour of C. elegans embryos. PMID:27004937
Optimized flow cytometry isolation of murine spermatocytes.
Gaysinskaya, Valeriya; Soh, Ina Y; van der Heijden, Godfried W; Bortvin, Alex
2014-06-01
Meiotic prophase I (MPI), is an initial stage of meiosis characterized by intricate homologous chromosome interactions, synapsis, and DNA recombination. These processes depend on the complex, but poorly understood early MPI events of homologous chromosome search, alignment, and pairing. Detailed molecular investigation of these early events requires isolation of individual MPI substages. Enrichment for Pachytene (P) and Diplotene (D) substages of late MPI was previously accomplished using flow cytometry. However, separation of early MPI spermatocytes, specifically, of Leptotene (L) and Zygotene (Z) substages, has been a challenge due to these cells' similar characteristics. In this report, we describe an optimized Hoechst-33342 (Hoechst)-based flow cytometry approach for isolating individual MPI populations from adult mouse testis. We get significant enrichment for individual L and Z spermatocytes, previously inseparable from each other, and optimize the isolation of other MPI substages. Our flow cytometry approach is a combination of three optimized strategies. The first is optimization of testis dissociation protocol that yields more consistent and reproducible testicular single cell suspension. The second involves optimization of flow cytometric gating protocol where a critical addition to the standard protocol for cell discrimination based on Hoechst fluorescence, involves a back-gating technique based on light scattering parameters. This step specifies selection of individual MPI substages. The third, is an addition of DNA content restriction to the gating protocol to minimize contamination from non-meiotic cells. Finally, we confirm significant enrichment of high-purity Preleptotene (PreL), L, Z, P, and D MPI spermatocytes using stage-specific marker distribution. The technique will facilitate understanding of the molecular events underlying MPI. PMID:24664803
Tearing mode in a neutral current sheet in a plasma flow
NASA Astrophysics Data System (ADS)
Gubchenko, V. M.
1982-09-01
The linear stage of the tearing mode is analyzed for a diffuse neutral current sheet in a plasma flow along the magnetic field. It follows from the dispersion characteristics derived that the flow tends to stabilize the tearing mode and gives rise to a drift phase velocity.
Maximizing Thermal Efficiency and Optimizing Energy Management (Fact Sheet)
Not Available
2012-03-01
Researchers at the Thermal Test Facility (TTF) on the campus of the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) in Golden, Colorado, are addressing maximizing thermal efficiency and optimizing energy management through analysis of efficient heating, ventilating, and air conditioning (HVAC) strategies, automated home energy management (AHEM), and energy storage systems.
Complex Dynamic Flows in Solar Flare Sheet Structures
NASA Technical Reports Server (NTRS)
McKenzie, David E.; Reeves, Katharine K.; Savage, Sabrina
2012-01-01
Observations of high-energy emission from solar flares often reveal the presence of large sheet-like structures, sometimes extending over a space comparable to the Sun's radius. Given that these structures are found between a departing coronal mass ejection and the post-eruption flare arcade, it is natural to associate the structure with a current sheet; though the relationship is unclear. Moreover, recent high-resolution observations have begun to reveal that the motions in this region are highly complex, including reconnection outflows, oscillations, and apparent wakes and eddies. We present a detailed first look at the complicated dynamics within this supra-arcade plasma, and consider implications for the interrelationship between the plasma and its embedded magnetic field.
Late Wisconsinan ice sheet flow across northern and central Vermont, USA
NASA Astrophysics Data System (ADS)
Wright, Stephen F.
2015-12-01
A compilation of over 2000 glacial striation azimuths across northern and central Vermont, northeastern USA, provides the basis for interpreting a sequence of ice flow directions across this area. The oldest striations indicate widespread ice flow to the southeast, obliquely across the mountains. Similarly oriented striations between northern Vermont and the ice sheet's terminus in the Gulf of Maine suggest that a broad area of southeast ice flow existed at the Last Glacial Maximum. Younger striations with more southerly azimuths on both the mountain ridgelines and within adjacent valleys indicate that ice sheet flow trajectories in most areas rotated from southeast to south, parallel to the North-South alignment of the mountains, as the ice sheet thinned. This transition in ice flow direction was time transgressive from south to north with the Green Mountains eventually separating a thick south-flowing lobe of ice in the Champlain Valley from a much thinner lobe of south-flowing ice east of the mountains. While this transition was taking place yet ice was still thick enough to flow across the mountains, ice flow along a narrow ˜65 km long section of the Green Mountains shifted to the southwest such that ice was flowing into the Champlain Valley. The most likely process driving this change was a limited period of fast ice flow in the Champlain Valley, a short-lived ice streaming event, that drew down the ice surface in the valley. The advancing ice front during this period of fast ice flow may be responsible for the Luzerne Readvance south of Glens Falls, New York. Valley-parallel striations across the area indicate strong topographic control on ice flow as the ice sheet thinned.
Seasonal Greenland Ice Sheet ice flow variations in regions of differing bed and surface topography
NASA Astrophysics Data System (ADS)
Sole, A. J.; Livingstone, S. J.; Rippin, D. M.; Hill, J.; McMillan, M.; Quincey, D. J.
2015-12-01
The contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise is uncertain. Observations reveal the important role of basal water in controlling ice-flow to the ice sheet margin. In Greenland, drainage of large volumes of surface meltwater to the ice sheet bed through moulins and hydrofracture beneath surface lakes dominates the subglacial hydrological system and provides an efficient means of moving mass and heat through the ice sheet. Ice surface and bed topography influence where meltwater can access the bed, and the nature of its subsequent flow beneath the ice. However, no systematic investigation into the influence of topographic variability on Greenland hydrology and dynamics exists. Thus, physical processes controlling storage and drainage of surface and basal meltwater, and the way these affect ice flow are not comprehensively understood. This presents a critical obstacle in efforts to predict the future evolution of the GrIS. Here we present high-resolution satellite mapping of the ice-surface drainage network (e.g. lakes, channels and moulins) and measurements of seasonal variations in ice flow in south west Greenland. The region is comprised of three distinct subglacial terrains which vary in terms of the amplitude and wavelength and thus the degree to which basal topography is reflected in the ice sheet surface. We find that the distribution of surface hydrological features is related to the transfer of bed topography to the ice sheet surface. For example, in areas of thinner ice and high bed relief, moulins occur more frequently and are more uniformly dispersed, indicating a more distributed influx of surface-derived meltwater to the ice sheet bed. We investigate the implications of such spatial variations in surface hydrology on seasonal ice flow rates.
NASA Astrophysics Data System (ADS)
Ishak, Anuar; Nazar, Roslinda; Pop, Ioan
2014-06-01
The steady mixed convection boundary layer flow through a stable stratified medium over a stretching vertical sheet is investigated. The velocity of the stretching sheet, the surface temperature and the ambient temperature are assumed to vary linearly with the distance from the leading edge. The transformed ordinary differential equations are solved numerically by the Keller-box method. The results indicate that the thermal stratification significantly affects the surface shear stress as well as the heat transfer rate at the surface. For the opposing flow, solution exists only for small magnitude of the buoyancy parameter.
The influence of thermal radiation on MHD flow of Maxwellian fluids above stretching sheets
NASA Astrophysics Data System (ADS)
Aliakbar, V.; Alizadeh-Pahlavan, A.; Sadeghy, K.
2009-03-01
Flow induced in a viscoelastic fluid by a linearly stretched sheet is investigated assuming that the fluid is Maxwellian and the sheet is subjected to a transverse magnetic field. The objective is to investigate the effects of parameters such as elasticity number, magnetic number, radiative heat transfer, Prandtl number, and Eckert number on the temperature field above the sheet. To do this, boundary layer theory will be used to simplify energy and momentum equations assuming that fluid physical/rheological properties remain constant. A suitable similarity transformation will be used to transform boundary layer equations from PDEs into ODEs. Homotopy analysis method (HAM) will be invoked to find an analytical solution for the temperature field above the sheet knowing the velocity profiles (see Alizadeh-Pahlavan et al. [Alizadeh-Pahlavan A, Aliakbar V, Vakili-Farahani F, Sadeghy K. MHD flows of UCM fluids above porous stretching sheets using two-auxiliary parameter homotopy analysis method. Commun. Nonlinear Sci Numer Simulat, in press]). The importance of manipulating the transverse velocity component, v, will be discussed on the temperature field above the sheet.
Motion of non-uniform double current-vortex sheets in magnetohydrodynamic flows
NASA Astrophysics Data System (ADS)
Matsuoka, Chihiro
2016-03-01
A nonlinear motion of vortex sheets with a non-uniform current is investigated using the vortex blob method. The fluid interface forms a double layered current-vortex sheet due to the boundary condition possessing the induction equation. We can prove that the current only flows on the interface and that does not appear in the bulk when we apply the initial magnetic field to be parallel to the interface. We show that the current induced on a vortex sheet leads to a strong amplification of the magnetic field, taking the motion of vortex sheets in magnetohydrodynamic Richtmyer-Meshkov instability as an example. When the initial Lorentz force term is large, an oscillation due to the Alfvén wave appears and the nonlinear growth is suppressed.
Ionospheric signatures of a plasma sheet rebound flow during a substorm onset
NASA Astrophysics Data System (ADS)
Juusola, L.; Kubyshkina, M.; Nakamura, R.; PitkäNen, T.; Amm, O.; Kauristie, K.; Partamies, N.; RèMe, H.; Snekvik, K.; Whiter, D.
2013-01-01
Magnetic reconnection in Earth's magnetotail produces fast earthward flows in the plasma sheet. Tailward flows are often observed associated with the earthward flows. Both return flow vortices at the flanks of an earthward flow channel and rebound of the earthward flow from the intense dipolar magnetic field of the inner magnetosphere have been shown to explain tailward flows observed near Earth. We combine plasma sheet measurements from Cluster with conjugate ground-based magnetic and auroral data to examine the development of earthward and tailward flow signatures during a substorm onset. We show for the first time observations of ionospheric signatures that appear to be associated with rebound flows. Because of the highly dynamic magnetotail configuration, special care is taken with the satellite footprint mapping. The ionospheric footprints produced by the event oriented AM02 model drift equatorward and poleward in response to tail magnetic field stretching and dipolarization, respectively. The footprint motion matches that of the ambient ionospheric structures, and the plasma flow measured by Cluster agrees with that inferred from the conjugate ionospheric observations, confirming the validity of the AM02 mapping. The ionospheric signatures of fast earthward flows during a substorm onset are shown to resemble the known signatures of quiet-time flows, including equatorward propagating auroral streamers inside a channel of enhanced poleward equivalent current. However, the large-scale dipolarization results in additional poleward expansion of the signatures, as has been predicted by simulations.
Application of GRACE to the Evaluation of an Ice Flow Model of the Greenland Ice Sheet
NASA Astrophysics Data System (ADS)
Schlegel, N.; Wiese, D. N.; Watkins, M. M.; Larour, E. Y.; Box, J. E.; Fettweis, X.; van den Broeke, M. R.; Morlighem, M.; Boening, C.; Seroussi, H. L.
2014-12-01
Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate estimates of ice flow sensitivity to climate change. Transient ice flow models are promising tools for estimating future ice sheet behavior. However, confidence in these types of future projections is low, especially because evaluation of model historical runs is so challenging due to the scarcity of continental-wide data for validation. For more than a decade, NASA's GRACE has continuously acquired time-variable measurements of the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The comparison highlights which regions of the ice sheet differ most from GRACE. Investigation of regional differences in trends and seasonal amplitudes between simulations forced with three different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows us to make conclusions about the relative contributions of various error sources in the model hindcast. This study constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and future rates of sea level rise. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Program and President's and Director's Fund Program.
Optimal Control of Flows in Moving Domains
NASA Astrophysics Data System (ADS)
Protas, Bartosz; Liao, Wenyuan; Glander, Donn
2006-11-01
This investigation concerns adjoint--based optimization of viscous incompressible flows (the Navier-Stokes problem) coupled with heat conduction involving change of phase (the Stefan problem) and occurring in domains with moving boundaries such as the free and solidification surfaces. This problem is motivated by optimization of advanced welding techniques used in automotive manufacturing. We characterize the sensitivity of a suitable cost functional defined for the system with respect to control (the heat input) using adjoint equations. Given that the shape of the domain is also a dependent variable, characterizing sensitivities necessitates the introduction of ``non-cylindrical'' calculus required to differentiate a cost functional defined on a variable domain. As a result, unlike the forward problem, the adjoint system is defined on a domain with a predetermined evolution in time and also involves ordinary differential equations defined on the domain boundary (``the adjoint transverse system''). We will discuss certain computational issues related to numerical solution of such adjoint problems.
Stagnation-point flow over a stretching/shrinking sheet in a nanofluid
2011-01-01
An analysis is carried out to study the steady two-dimensional stagnation-point flow of a nanofluid over a stretching/shrinking sheet in its own plane. The stretching/shrinking velocity and the ambient fluid velocity are assumed to vary linearly with the distance from the stagnation point. The similarity equations are solved numerically for three types of nanoparticles, namely copper, alumina, and titania in the water-based fluid with Prandtl number Pr = 6.2. The skin friction coefficient, Nusselt number, and the velocity and temperature profiles are presented graphically and discussed. Effects of the solid volume fraction φ on the fluid flow and heat transfer characteristics are thoroughly examined. Different from a stretching sheet, it is found that the solutions for a shrinking sheet are non-unique. PMID:22151965
2012-01-01
In this work, we study the flow and heat transfer characteristics of a viscous nanofluid over a nonlinearly stretching sheet in the presence of thermal radiation, included in the energy equation, and variable wall temperature. A similarity transformation was used to transform the governing partial differential equations to a system of nonlinear ordinary differential equations. An efficient numerical shooting technique with a fourth-order Runge-Kutta scheme was used to obtain the solution of the boundary value problem. The variations of dimensionless surface temperature, as well as flow and heat-transfer characteristics with the governing dimensionless parameters of the problem, which include the nanoparticle volume fraction ϕ, the nonlinearly stretching sheet parameter n, the thermal radiation parameter NR, and the viscous dissipation parameter Ec, were graphed and tabulated. Excellent validation of the present numerical results has been achieved with the earlier nonlinearly stretching sheet problem of Cortell for local Nusselt number without taking the effect of nanoparticles. PMID:22520273
Multiphase flow of the late Wisconsinan Cordilleran ice sheet in Western Canada
Stumpf, A.J.; Broster, B.E.; Levson, V.M.
2000-01-01
In central British Columbia, ice flow during the late Wisconsinan Fraser glaciation (ca. 25-10 ka) occurred in three phases. The ice expansion phase occurred during an extended period when glaciers flowed westward to the Pacific Ocean and east-southeastward onto the Nechako Plateau from ice centers in the Skeena, Hazelton, Coast, and Omineca Mountains. Initially, glacier flow was confined by topography along major valleys, but eventually piedmont and montane glaciers coalesced to form an integrated glacier system, the Cordilleran ice sheet. In the maximum phase, a Cordilleran ice divide developed over the Nechako Plateau to 300 km inland from the Pacific coast. At this time, the surface of the ice sheet extended well above 2500 m above sea level, and flowed westward over the Skeena, Hazelton, and Coast Mountains onto the continental shelf, and eastward across the Rocky Mountains into Alberta. In the late glacial phase, a rapid rise of the equilibrium line caused ice lobes to stagnate in valleys, and restricted accumulation centers to high mountains. Discordant directions in ice flow are attributed to fluctuations of the ice divide representing changes in the location of accumulation centers and ice thickness. Ice centers probably shifted in response to climate, irregular growth in the ice sheet, rapid calving, ice streaming, and drainage of proglacial and subglacial water bodies. Crosscutting ice-flow indicators and preservation of early (valley parallel) flow features in areas exposed to later (cross-valley) glacier erosion indicate that the ice expansion phase was the most erosive and protracted event.
Large-scale laboratory measurements of sheet flow sediment transport in the swash zone
NASA Astrophysics Data System (ADS)
Lanckriet, T. M.; Puleo, J. A.; Foster, D. L.
2013-12-01
Existing sediment transport models show poor predictive quality when applied to the swash zone, indicating that the underlying processes of swash zone sediment transport are not yet fully understood. The recognition that more detailed measurements are needed to improve understanding of swash-zone processes has led to several recent innovations in swash-zone measurement techniques. One of these innovative measurement techniques, the Conductivity Concentration Profiler (CCP), was developed to address the issue of near-bed (sheet flow) sediment transport, which is believed to be an important part of the overall swash-zone sediment transport. Measurements of sheet flow processes in the swash zone from the Barrier Dynamics Experiment (Bardex-II) are presented. The aim of this study was to investigate the dynamics of a coastal barrier system and develop an increased understanding of cross-shore sediment transport processes in the nearshore zone of sandy beaches. A 70-m long, near-prototype scale sandy barrier was constructed in a large wave flume facility and equipped with over 200 sensors to measure hydrodynamics and sediment processes ranging from the shoaling-wave zone to the back barrier. CCP sensors were deployed at three locations in the swash zone as part of the ';swash and berm dynamics' work package. Onshore-directed pressure gradients, observed during the initial stages of uprush, enhanced sediment mobilization. The combination of near-bed sediment mobilization due to pressure gradients (known as plug flow) and shear stress (sheet flow) is examined. Sediment load in the sheet flow layer is also compared to suspended load and total load measured using an array of optical backscatter sensors. The sheet flow layer thickness is compared to hydrodynamic forcing such as bed shear stress and the effect of groundwater exchange.
Magnetohydrodynamic stagnation point flow towards a stretching vertical sheet in a micropolar fluid
NASA Astrophysics Data System (ADS)
Ishak, A.; Nazar, R.; Pop, I.
2007-03-01
The analysis of steady two-dimensional stagnation point flow of an incompressible micropolar and electrically conducting fluid subject to a transverse uniform magnetic field towards a stretching vertical sheet is investigated when the sheet is stretched in its own plane with a velocity and a temperature proportional to the distance from the stagnation point. The governing system of partial differential equations is transformed to ordinary differential equations, which then are solved numerically using a finite difference scheme known as the Keller-box method. The velocity, microrotation and temperature distributions as well as the skin friction coefficient and the local Nusselt number are obtained for various parameters. Both the assisting and the opposing buoyant flows are considered. It is found that dual solutions exist for the opposing flow, for some regions of the buoyancy parameter, while for the assisting flow the solution is unique. Tables 3, Figs 14, Refs 26.
Analytical Solution to the MHD Flow of Micropolar Fluid Over a Linear Stretching Sheet
NASA Astrophysics Data System (ADS)
Siddheshwar, P. G.; Mahabaleshwar, U. S.
2015-05-01
The flow due to a linear stretching sheet in a fluid with suspended particles, modeled as a micropolar fluid, is considered. All reported works on the problem use numerical methods of solution or a regular perturbation technique. An analytical solution is presented in the paper for the coupled non-linear differential equations with inhomogeneous boundary conditions.
Evaluation of alternative flow sheets for upgrade of the Process Waste Treatment Plant
Robinson, S.M.
1991-04-01
Improved chemical precipitation and/or ion-exchange (IX) methods are being developed at the Oak Ridge National Laboratory (ORNL) in an effort to reduce waste generation at the Process Waste Treatment Plant (PWTP). A wide variety of screening tests were performed on potential precipitation techniques and IX materials on a laboratory scale. Two of the more promising flow sheets have been tested on pilot and full scales. The data were modeled to determine the operating conditions and waste generation at plant-scale and used to develop potential flow sheets for use at the PWTP. Each flow sheet was evaluated using future-valve economic analysis and performance ratings (where numerical values were assigned to costs, process flexibility and simplicity, stage of development, waste reduction, environmental and occupational safety, post-processing requirements, and final waste form). The results of this study indicated that several potential flow sheets should be considered for further development, and more detailed cost estimates should be made before a final selection is made for upgrade of the PWTP. 19 refs., 52 figs., 22 tabs.
Numerical analysis of magnetic field effects on Eyring-Powell fluid flow towards a stretching sheet
NASA Astrophysics Data System (ADS)
Sher Akbar, Noreen; Ebaid, Abdelhalim; Khan, Z. H.
2015-05-01
In the present article, we have examined the two dimensional MHD flow of Eyring-Powell fluid model towards a stretching sheet. The governing equations of Eyring-Powell fluid are modeled and then simplified by using boundary layer approach and similarity transformations and then solved numerically using implicit finite difference method. It was found that the increase in the intensity of the magnetic field as well as Eyring-Powell fluid parameter γ shows resistance to the flow.
A Hybrid Vortex Sheet / Point Vortex Model for Unsteady Separated Flows
NASA Astrophysics Data System (ADS)
Darakananda, Darwin; Eldredge, Jeff D.; Colonius, Tim; Williams, David R.
2015-11-01
The control of separated flow over an airfoil is essential for obtaining lift enhancement, drag reduction, and the overall ability to perform high agility maneuvers. In order to develop reliable flight control systems capable of realizing agile maneuvers, we need a low-order aerodynamics model that can accurately predict the force response of an airfoil to arbitrary disturbances and/or actuation. In the present work, we integrate vortex sheets and variable strength point vortices into a method that is able to capture the formation of coherent vortex structures while remaining computationally tractable for control purposes. The role of the vortex sheet is limited to tracking the dynamics of the shear layer immediately behind the airfoil. When parts of the sheet develop into large scale structures, those sections are replaced by variable strength point vortices. We prevent the vortex sheets from growing indefinitely by truncating the tips of the sheets and transfering their circulation into nearby point vortices whenever the length of sheet exceeds a threshold. We demonstrate the model on a variety of canonical problems, including pitch-up and impulse translation of an airfoil at various angles of attack. Support by the U.S. Air Force Office of Scientific Research (FA9550-14-1-0328) with program manager Dr. Douglas Smith is gratefully acknowledged.
Optimal propulsive flapping in Stokes flows.
Was, Loïc; Lauga, Eric
2014-03-01
Swimming fish and flying insects use the flapping of fins and wings to generate thrust. In contrast, microscopic organisms typically deform their appendages in a wavelike fashion. Since a flapping motion with two degrees of freedom is able, in theory, to produce net forces from a time-periodic actuation at all Reynolds numbers, we compute in this paper the optimal flapping kinematics of a rigid spheroid in a Stokes flow. The hydrodynamics for the force generation and energetics of the flapping motion is solved exactly. We then compute analytically the gradient of a flapping efficiency in the space of all flapping gaits and employ it to derive numerically the optimal flapping kinematics as a function of the shape of the flapper and the amplitude of the motion. The kinematics of optimal flapping are observed to depend weakly on the flapper shape and are very similar to the figure-eight motion observed in the motion of insect wings. Our results suggest that flapping could be a exploited experimentally as a propulsion mechanism valid across the whole range of Reynolds numbers. PMID:24343130
NASA Astrophysics Data System (ADS)
Chauchat, J.; Revil-Baudard, T.; Hurther, D.
2014-12-01
Sheet flow is believed to be a major process for morphological evolution of natural systems. An important research effort has been dedicated to laboratory and numerical studies of sheet flow regime that have allowed to make some progress in the understanding of the underlying physical processes. Recent advances made in high resolution measurement techniques allows to give new insights into the small scale physical processes. In this contribution, a novel uniform and steady sheet flow dataset based on an Acoustic Concentration and Velocity Profiler (ACVP) is presented. Profile of colocated velocities (streamwise and wall-normal) and sediment concentration has been measured at high-resolution (3 mm ; 78 Hz for the velocities and 4.9 Hz for the concentration). The measured profiles extend over the whole water column, from the free surface down to the fixed bed and an ensemble averaging over eleven realisations of the same experimental conditions has been used to obtain mean profiles of streamwise velocity, concentration, sediment flux and turbulent shear stress. The present experiment corresponds to a Shields number of θ=0.44 and a suspension number of ws/u*=1.1 corresponding to the lower limit of the no-suspension sheet flow regime. The analysis of the mixing length profile allows to identify two layers, a dilute suspension layer dominated by turbulence and a dense moving bed layer dominated by granular interactions. Our measurements show that the Von Karman parameter is reduced by a factor of more than two and that the Schmidt number is almost constant with a mean value of σs=0.44. Frictional and collisional interactions are encountered in the bed layer. Frictional interactions dominate close to the fixed bed interface whereas collisional interactions seems to control the flow at the transition between the dense and dilute layers. The relevancy of different constitutive laws for two-phase flow models are discussed.
Annular flow optimization: A new integrated approach
Maglione, R.; Robotti, G.; Romagnoli, R.
1997-07-01
During the drilling stage of an oil and gas well the hydraulic circuit of the mud assumes great importance with respect to most of the numerous and various constituting parts (mostly in the annular sections). Each of them has some points to be satisfied in order to guarantee both the safety of the operations and the performance optimization of each of the single elements of the circuit. The most important tasks for the annular part of the drilling hydraulic circuit are the following: (1) Maximum available pressure to the last casing shoe; (2) avoid borehole wall erosions; and (3) guarantee the hole cleaning. A new integrated system considering all the elements of the annular part of the drilling hydraulic circuit and the constraints imposed from each of them has been realized. In this way the family of the flow parameters (mud rheology and pump rate) satisfying simultaneously all the variables of the annular section has been found. Finally two examples regarding a standard and narrow annular section (slim hole) will be reported, showing briefly all the steps of the calculations until reaching the optimum flow parameters family (for that operational condition of drilling) that satisfies simultaneous all the flow parameters limitations imposed by the elements of the annular section circuit.
Equivalent Relaxations of Optimal Power Flow
Bose, S; Low, SH; Teeraratkul, T; Hassibi, B
2015-03-01
Several convex relaxations of the optimal power flow (OPF) problem have recently been developed using both bus injection models and branch flow models. In this paper, we prove relations among three convex relaxations: a semidefinite relaxation that computes a full matrix, a chordal relaxation based on a chordal extension of the network graph, and a second-order cone relaxation that computes the smallest partial matrix. We prove a bijection between the feasible sets of the OPF in the bus injection model and the branch flow model, establishing the equivalence of these two models and their second-order cone relaxations. Our results imply that, for radial networks, all these relaxations are equivalent and one should always solve the second-order cone relaxation. For mesh networks, the semidefinite relaxation and the chordal relaxation are equally tight and both are strictly tighter than the second-order cone relaxation. Therefore, for mesh networks, one should either solve the chordal relaxation or the SOCP relaxation, trading off tightness and the required computational effort. Simulations are used to illustrate these results.
Design optimization of natural laminar flow bodies in compressible flow
NASA Technical Reports Server (NTRS)
Dodbele, Simha S.
1992-01-01
An optimization method has been developed to design axisymmetric body shapes such as fuselages, nacelles, and external fuel tanks with increased transition Reynolds numbers in subsonic compressible flow. The new design method involves a constraint minimization procedure coupled with analysis of the inviscid and viscous flow regions and linear stability analysis of the compressible boundary-layer. In order to reduce the computer time, Granville's transition criterion is used to predict boundary-layer transition and to calculate the gradients of the objective function, and linear stability theory coupled with the e(exp n)-method is used to calculate the objective function at the end of each design iteration. Use of a method to design an axisymmetric body with extensive natural laminar flow is illustrated through the design of a tiptank of a business jet. For the original tiptank, boundary layer transition is predicted to occur at a transition Reynolds number of 6.04 x 10(exp 6). For the designed body shape, a transition Reynolds number of 7.22 x 10(exp 6) is predicted using compressible linear stability theory coupled with the e(exp n)-method.
Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall
NASA Astrophysics Data System (ADS)
Doyle, Samuel H.; Hubbard, Alun; van de Wal, Roderik S. W.; Box, Jason E.; van As, Dirk; Scharrer, Kilian; Meierbachtol, Toby W.; Smeets, Paul C. J. P.; Harper, Joel T.; Johansson, Emma; Mottram, Ruth H.; Mikkelsen, Andreas B.; Wilhelms, Frank; Patton, Henry; Christoffersen, Poul; Hubbard, Bryn
2015-08-01
Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.
Ballooning instability of the earth's plasma sheet region in the presence of parallel flow
NASA Technical Reports Server (NTRS)
Lakhina, G. S.; Hameiri, E.; Mond, M.
1990-01-01
Stability of the plasma sheet and plasma sheet boundary layer against the ballooning mode instability is investigated. The equilibrium state of a two-dimensional plasma sheet configuration with parallel sheared flow is modeled. This equilibrium is shown to be ballooning unstable when delta-W is not positive definite, where delta-W is the potential energy. The eigenmode structure of the ballooning mode is found by imposing the boundary conditions that the waves are totally reflected from the ionosphere, and that no waves are coming in from infinity. The eigenmode structure of the unstable balloning modes is highly oscillatory, extending beyond about 100 R(E). The ballooning modes are thus a possible candidate for explaining the MHD waves and other dynamical events observed in the magnetotail by ISEE 3 and other spacecraft.
Shape optimization of a sheet swimming over a thin liquid layer
Wilkening, J.; Hosoi, A.E.
2008-12-10
Motivated by the propulsion mechanisms adopted by gastropods, annelids and other invertebrates, we consider shape optimization of a flexible sheet that moves by propagating deformation waves along its body. The self-propelled sheet is separated from a rigid substrate by a thin layer of viscous Newtonian fluid. We use a lubrication approximation to model the dynamics and derive the relevant Euler-Lagrange equations to simultaneously optimize swimming speed, efficiency and fluid loss. We find that as the parameters controlling these quantities approach critical values, the optimal solutions become singular in a self-similar fashion and sometimes leave the realm of validity of the lubrication model. We explore these singular limits by computing higher order corrections to the zeroth order theory and find that wave profiles that develop cusp-like singularities are appropriately penalized, yielding non-singular optimal solutions. These corrections are themselves validated by comparison with finite element solutions of the full Stokes equations, and, to the extent possible, using recent rigorous a-priori error bounds.
Shape optimization of a sheet swimming over a thin liquid layer
NASA Astrophysics Data System (ADS)
Wilkening, Jon; Hosoi, A. E.
Motivated by the propulsion mechanisms adopted by gastropods, annelids and other invertebrates, we consider shape optimization of a flexible sheet that moves by propagating deformation waves along its body. The self-propelled sheet is separated from a rigid substrate by a thin layer of viscous Newtonian fluid. We use a lubrication approximation to model the dynamics and derive the relevant Euler-Lagrange equations to simultaneously optimize swimming speed, efficiency and fluid loss. We find that as the parameters controlling these quantities approach critical values, the optimal solutions become singular in a self-similar fashion and sometimes leave the realm of validity of the lubrication model. We explore these singular limits by computing higher-order corrections to the zeroth order theory and find that wave profiles that develop cusp-like singularities are appropriately penalized, yielding non-singular optimal solutions. These corrections are themselves validated by comparison with finite element solutions of the full Stokes equations, and, to the extent possible, using recent rigorous a priori error bounds.
Opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment
NASA Astrophysics Data System (ADS)
Malhotra, Vinayak; Kumar, Chenthil; Kumar, Amit
2013-10-01
In this work a numerical study has been carried out to gain physical insight into the phenomena of opposed flow flame spread over an array of thin solid fuel sheets in a microgravity environment. The two-dimensional (2D) simulations show that the flame spread rates for the multiple-fuel configuration are higher than those for the flame spreading over a single fuel sheet. This is due to reduced radiation losses from the flame and increased heat feedback to the solid fuel. The flame spread rate exhibits a non-monotonic variation with decrease in the interspace distance between the fuel sheets. Higher radiation heat feedback primarily as gas/flame radiation was found to be responsible for the increase in the flame spread rate with the reduction of the interspace distance. It was noted that as the interspace distance between the fuel sheets was reduced below a certain value, no steady solution could be obtained. However, at very small interspace distances, steady state spread rates were obtained. Here, due to oxygen starvation the flame spread rate decreased and eventually at some interspace distance the flame extinguished. With fuel emittance (equal to absorptance) reduced to '0' the flame spread rate was nearly independent of the interspace distance, except at very small distances where the flame spread rate dropped due to oxygen starvation. A flame extinction plot with the extinction oxygen level was constructed for the multiple-fuel configuration at various interspace distances. The default fuel with an emittance of 0.92 was found to be more flammable in the multiple-fuel configuration than in a single fuel sheet configuration. For a fuel emittance equal to zero, the extinction oxygen limit decreases for both the single and the multiple fuel sheet configurations. However, the two flammability curves cross over at a certain fuel separation distance. The multiple-fuel configurations become less flammable compared to the single fuel sheet configuration below a certain
Power flow and PRS optimization on Phoenix
NASA Astrophysics Data System (ADS)
Terry, Robert E.; Cochran, Frederick L.
1994-03-01
The DNA Phoenix program has investigated the power flow in the front end magnetically insulated transmission line (MITL) and PRS load assembly, to identify any losses, and model them, and the optimum injection angle and mass loading for a specific puff gas nozzle assembly. An optimum PRS mass loading can convert about 10-15% of the energy delivered to the front end into load kinetic energy over a range of 4.65 - 5.7 nH of initial PRS loading inductance. Specific kinetic energy per ion tends to fall off monotonically as the PRS length exceeds 4.5 cm. The gas puff optimization investigated nozzle designs which could optimize the uniformity of the implosion through high Mach number and tilting. The best yields for Argon were found at 12 deg for a Mach 4 nozzle, and 7.5 deg for a Mach 5 nozzle. The yield at the optimum tilt angle does not vary strongly with Mach number.
Active current sheets and hot flow anomalies in Mercury's bow shock
NASA Astrophysics Data System (ADS)
Uritsky, V. M.; Slavin, J. A.; Boardsen, S. A.; Sundberg, T.; Raines, J. M.; Anderson, B. J.; Korth, H.
2012-12-01
Hot flow anomalies (HFAs) represent a subset of heliospheric current sheets interacting with planetary bow shocks. They are typically formed when the normal component of the motional (convective) electric field is directed toward the embedded current sheet on at least one side. The core region of an HFA contains hot and highly deflected ion flows and rather low and turbulent magnetic field. In this talk, we report the first observations of HFA-like events at Mercury. Using the data from the orbital phase of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, we identify a representative ensemble of active current sheets magnetically connected to Mercury's bow shock. We show that some of these events exhibit unambiguous signatures of HFAs similar to those observed at other planets, and present their key physical characteristics. Our analysis suggests that Mercury's bow shock does not only mediate the flow of supersonic solar wind plasma but also provides conditions for local particle acceleration and heating as predicted by previous numerical simulations. Together with earlier studies of HFA activity at Earth, Venus, and Saturn, our results confirm that hot flow anomalies could be a common property of planetary bow shocks.
An analysis of the acoustic energy in a flow duct with a vortex sheet
NASA Astrophysics Data System (ADS)
Boij, Susann
2009-03-01
Modelling the acoustic scattering and absorption at an area expansion in a flow duct requires the incorporation of the flow-acoustic interaction. One way to quantify the interaction is to study the energy in the incident and the scattered field respectively. If the interaction is strong, energy may be transferred between the acoustic and the main flow field. In particular, shear layers, that may be the result of the flow separation, are unstable to low frequency perturbations such as acoustic waves. The vortex sheet model is an analytical linear acoustic model, developed to study scattering of acoustic waves in duct with sharp edges including the interaction with primarily the separated flows that arise at sharp edges and corners. In the model the flow field at an area expansion in a duct is described as a jet issuing into the larger part of the duct. In this paper, the flow-acoustic interaction is described in terms of energy flow. The linear convective wave equation is solved for a two-dimensional, rectangular flow duct geometry. The resulting modes are classified as "hydrodynamic" and "acoustic" when separating the acoustic energy from the part of the energy arising from the steady flow field. In the downstream duct, the set of modes for this complex flow field are not orthogonal. For small Strouhal numbers, the plane wave and the two hydrodynamic waves are all plane, although propagating with different wave speeds. As the Strouhal numbers increases, the hydrodynamic modes changes to get a shape where the amplitude is concentrated near the vortex sheet. In an intermediate Strouhal number region, the mode shape of the first higher order mode is very similar to the damped hydrodynamic mode. A physical interpretation of this is that we have a strong coupling between the flow field and the acoustic field when the modes are non-orthogonal. Energy concepts for this duct configuration and mean flow profile are introduced. The energy is formulated such that the vortex
Stability analysis of stagnation-point flow over a stretching/shrinking sheet
NASA Astrophysics Data System (ADS)
Awaludin, I. S.; Weidman, P. D.; Ishak, Anuar
2016-04-01
The stagnation point flow over a linearly stretching or shrinking sheet is considered in the present study. The transformed ordinary differential equations are solved numerically. Dual solutions are possible for the shrinking case, while the solution is unique for the stretching case. For the shrinking case, a linear temporal stability analysis is performed to determine which one of the solution is stable and thus physically reliable.
Visualization of internal flows of complex geometry using three-dimensional dynamical laser sheets
NASA Astrophysics Data System (ADS)
Prenel, J.-P.; Porcar, R.; Diemunsch, G.; Hostache, G.
1986-12-01
An extension of a previous visualization method (Prenel et al., 1986) is described in which three-dimensional light sheets obtained by sweeping of a laser beam are used to analyze internal flows of arbitrary geometry, with application to the testing of the ducts of thermal machines. The example of a variable circular test section with an elbow bend demonstrates the ability of the present method to successfully follow the evolution of a fluid in a channel of arbitrary form. Various aerodynamic parameters including position and dimension of the vortex flow, and dead zones and recirculations, are easily analyzed.
Khan, Junaid Ahmad; Mustafa, Meraj; Hayat, Tasawar; Alsaedi, Ahmed
2014-01-01
This article studies the viscous flow and heat transfer over a plane horizontal surface stretched non-linearly in two lateral directions. Appropriate wall conditions characterizing the non-linear variation in the velocity and temperature of the sheet are employed for the first time. A new set of similarity variables is introduced to reduce the boundary layer equations into self-similar forms. The velocity and temperature distributions are determined by two methods, namely (i) optimal homotopy analysis method (OHAM) and (ii) fourth-fifth-order Runge-Kutta integration based shooting technique. The analytic and numerical solutions are compared and these are found in excellent agreement. Influences of embedded parameters on momentum and thermal boundary layers are sketched and discussed. PMID:25198696
Khan, Junaid Ahmad; Mustafa, Meraj; Hayat, Tasawar; Alsaedi, Ahmed
2014-01-01
This article studies the viscous flow and heat transfer over a plane horizontal surface stretched non-linearly in two lateral directions. Appropriate wall conditions characterizing the non-linear variation in the velocity and temperature of the sheet are employed for the first time. A new set of similarity variables is introduced to reduce the boundary layer equations into self-similar forms. The velocity and temperature distributions are determined by two methods, namely (i) optimal homotopy analysis method (OHAM) and (ii) fourth-fifth-order Runge-Kutta integration based shooting technique. The analytic and numerical solutions are compared and these are found in excellent agreement. Influences of embedded parameters on momentum and thermal boundary layers are sketched and discussed. PMID:25198696
Effect of material flow on joint strength in activation spot joining of Al alloy and steel sheets
NASA Astrophysics Data System (ADS)
Watanabe, Goro; Yogo, Yasuhiro; Takao, Hisaaki
2014-08-01
A new joining method for dissimilar metal sheets was developed where a rotated consumable rod of Al alloy is pressed onto an Al alloy sheet at the part overlapped with a mild steel sheet. The metal flow in the joining region is increased by the through-hole in the Al sheet and consumable Al rod. The rod creates the joint interface and pads out of the thinly joined parts through pressing. This produces a higher joint strength than that of conventional friction stir spot welding. Measurements of the joint interface showed the presence of a 5-10 nm thick amorphous layer consisting of Al and Mg oxides.
Subglacial lake and meltwater flow predictions of the last North American and European Ice Sheets
NASA Astrophysics Data System (ADS)
Livingstone, S. J.; Clark, C. D.; Tarasov, L.
2012-04-01
There is increasing recognition that subglacial lakes act as key components within the ice sheet system, capable of influencing ice-sheet topography, ice volume and ice flow. The subglacial water systems themselves are recognised as being both active and dynamic, with large discharges of meltwater capable of flowing down hydrological pathways both between lakes and to the ice-sheet margins. At present, much glaciological research is concerned with the role of modern subglacial lake systems in Antarctica. Another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath ice sheets of the last glaciation. Investigation of such palaeo-subglacial lakes offers significant advantages because we have comprehensive information about the bed properties, they are much more accessible and we can examine and sample the sediments with ease. If we can find palaeo-subglacial lakes then we have the potential to advance understanding with regard to the topographic context and hydrological pathways that the phenomena form a part of; essentially we gain spatial and sedimentological information in relation to investigations of contemporary subglacial lakes and lose out on the short-time dynamics. In this work we present predictions of palaeo-subglacial lakes and meltwater drainage pathways under the former European and North American ice sheets during the last glaciation. We utilise data on the current topography and seafloor bathymetry, and elevation models of the ice and ground surface topography (interpolated to a 5 km grid) to calculate the hydraulic potential surface at the ice-sheet bed. Meltwater routing algorithms and the flooding of local hydraulic minima allow us to predict subglacial channels and lakes respectively. Given that specific ice-surface and bed topographies are only known from modelled outputs, and thus contain significant uncertainty, we utilise many such outputs to examine
Huysken, K.T.; Vogel, T.A. . Dept. of Geological Sciences)
1992-01-01
Small ash-flow layers directly underlying the voluminous Rainier Mesa ash-flow sheet are chemically equivalent to the overlying ash-flow. However, chemical variability of these precaldera-collapse pyroclastic deposits indicates they could not have erupted from the large volume Rainier Mesa Member (RMM) magma body. The RMM is a voluminous chemically and mineralogically layered and zoned ash-flow sheet. Directly underlying the RMM is a sequence of tephra-fall deposits interbedded with thin ash-flow layers, traditionally interpreted as pre-caldera-collapse deposits from the large magma body. Chemical comparison of 14 thin flows with the overlying RMM was made in order to decipher the relationship between earlier erupted ash-flow layers and the large ash-flow sheet. Within each thin ash-flow layer, there is substantial variation in major, trace, and REE concentrations over a thickness of only 0.5 to 5 m. The extremely small volume of pre-Rainier Mesa ash-flow layers would represent a negligible volume of the magma body. The observed chemical zoning would not occur if these small volume deposits erupted from the RMM magma body. Major and trace element variation among the small ash-flow layers spans that of the entire high-silica portion of the RMM ash-flow sheet, which makes up 90% of the total volume of the ash-flow. Moreover, REE concentrations among the thin ash-flow layers are as variable as the REE concentrations of the entire overlying ash-flow sheet. Because there is significant chemical variation both within and among small ash-flow layers underlying the RMM, the authors reject the possibility of a larger differentiating magma body as the source of the small pre-Rainier ash-flow layers.
Thermodynamic Optimization of Flow Geometry in Mechanical and Civil Engineering
NASA Astrophysics Data System (ADS)
Bejan, Adrian; Lorente, Sylvie
2001-12-01
Recent developments in thermodynamic optimization are reviewed by focusing on the generation of optimal geometric form (shape, structure, topology) in flow systems. The flow configuration is free to vary. The principle that generates geometric form is the pursuit of maximum global performance (e.g., minimum flow resistance, minimum irreversibility) subject to global finiteness constraints (volume, weight, time). The resulting structures constructed in this manner have been named constructal designs. The thought that the same objective and constraints principle accounts for the optimally shaped flow paths that occur in natural systems (animate and inanimate) has been named constructal theory. Examples of large classes of applications are drawn from various sectors of mechanical and civil engineering: the distribution of heat transfer area in power plants, optimal sizing and shaping of flow channels and fins, optimal aspect ratios of heat exchanger core structures, aerodynamic and hydrodynamic shapes, tree-shaped assemblies of convective fins, treeshaped networks for fluid flow and other currents, optimal configurations for streams that undergo bifurcation or pairing, insulated pipe networks for the distribution of hot water and exergy over a fixed territory, and distribution networks for virtually everything that moves in society (goods, currency, information). The principle-based generation of flow geometry unites the thermodynamic optimization developments known in mechanical engineering with lesser known applications in civil engineering and social organization. This review extends thermodynamics, because it shows how thermodynamic principles of design optimization account for the development of optimal configurations in civil engineering and social organization.
Wang, Zhongqi; Yang, Bo; Kang, Yonggang; Yang, Yuan
2016-01-01
Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method. PMID:27127499
Wang, Zhongqi; Yang, Bo; Kang, Yonggang; Yang, Yuan
2016-01-01
Fixture plays an important part in constraining excessive sheet metal part deformation at machining, assembly, and measuring stages during the whole manufacturing process. However, it is still a difficult and nontrivial task to design and optimize sheet metal fixture locating layout at present because there is always no direct and explicit expression describing sheet metal fixture locating layout and responding deformation. To that end, an RBF neural network prediction model is proposed in this paper to assist design and optimization of sheet metal fixture locating layout. The RBF neural network model is constructed by training data set selected by uniform sampling and finite element simulation analysis. Finally, a case study is conducted to verify the proposed method. PMID:27127499
connecting the dots between Greenland ice sheet surface melting and ice flow dynamics (Invited)
NASA Astrophysics Data System (ADS)
Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.
2013-12-01
This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity
Khodabakhshi, F.; Kazeminezhad, M. Kokabi, A.H.
2012-07-15
Constrained groove pressing as a severe plastic deformation method is utilized to produce ultra-fine grained low carbon steel sheets. The ultra-fine grained sheets are joined via resistance spot welding process and the characteristics of spot welds are investigated. Resistance spot welding process is optimized for welding of the sheets with different severe deformations and their results are compared with those of as-received samples. The effects of failure mode and expulsion on the performance of ultra-fine grained sheet spot welds have been investigated in the present paper and the welding current and time of resistance spot welding process according to these subjects are optimized. Failure mode and failure load obtained in tensile-shear test, microhardness, X-ray diffraction, transmission electron microscope and scanning electron microscope images have been used to describe the performance of spot welds. The region between interfacial to pullout mode transition and expulsion limit is defined as the optimum welding condition. The results show that optimum welding parameters (welding current and welding time) for ultra-fine grained sheets are shifted to lower values with respect to those for as-received specimens. In ultra-fine grained sheets, one new region is formed named recrystallized zone in addition to fusion zone, heat affected zone and base metal. It is shown that microstructures of different zones in ultra-fine grained sheets are finer than those of as-received sheets. - Highlights: Black-Right-Pointing-Pointer Resistance spot welding process is optimized for joining of UFG steel sheets. Black-Right-Pointing-Pointer Optimum welding current and time are decreased with increasing the CGP pass number. Black-Right-Pointing-Pointer Microhardness at BM, HAZ, FZ and recrystallized zone is enhanced due to CGP.
NASA Astrophysics Data System (ADS)
Liang, J.; Ni, B.; Cully, C. M.; Donovan, E. F.; Thorne, R. M.; Angelopoulos, V.
2012-03-01
In this study we perform a statistical survey of the extremely-low-frequency wave activities associated with fast earthward flows in the mid-tail central plasma sheet (CPS) based upon THEMIS measurements. We reveal clear trends of increasing wave intensity with flow enhancement over a broad frequency range, from below fLH (lower-hybrid resonant frequency) to above fce (electron gyrofrequency). We mainly investigate two electromagnetic wave modes, the lower-hybrid waves at frequencies below fLH, and the whistler-mode waves in the frequency range fLH < f < fce. The waves at f < fLH dramatically intensify during fast flow intervals, and tend to contain strong electromagnetic components in the high-plasma-beta CPS region, consistent with the theoretical expectation of the lower-hybrid drift instability in the center region of the tail current sheet. ULF waves with very large perpendicular wavenumber might be Doppler-shifted by the flows and also partly contribute to the observed waves in the lower-hybrid frequency range. The fast flow activity substantially increases the occurrence rate and peak magnitude of the electromagnetic waves in the frequency range fLH < f < fce, though they still tend to be short-lived and sporadic in occurrence. We also find that the electron pitch-angle distribution in the mid-tail CPS undergoes a variation from negative anisotropy (perpendicular temperature smaller than parallel temperature) during weak flow intervals, to more or less positive anisotropy (perpendicular temperature larger than parallel temperature) during fast flow intervals. The flow-related electromagnetic whistler-mode wave tends to occur in conjunction with positive electron anisotropy.
NASA Astrophysics Data System (ADS)
Jafar, Khamisah; Nazar, Roslinda; Ishak, Anuar; Hamzah, Firdaus Mohamad
2015-09-01
This paper considers a numerical investigation on the steady laminar two-dimensional MHD stagnation-point flow and heat transfer of an incompressible viscous fluid impinging normal to an exponentially stretching/shrinking flat sheet in the presence of a non-uniform magnetic field applied in a direction normal to the flat sheet. The sheet surface temperature is assumed to also vary exponentially with the distance from the stagnation-point. The governing system of partial differential equations is first transformed into ordinary differential equations, and solved numerically using an implicit finite-difference scheme known as the Keller-box method. The effects of the stretching/shrinking parameter ɛ and the magnetic parameter on the flow field and heat transfer characteristics are discussed. It is found that the magnitude of the skin friction coefficient |f″(o ) | , and the local Nusselt number -θ'(0 ) increase with both the magnetic parameter M and the stretching/shrinking parameter ɛ. For the shrinking case, it is found that there is a minimum value ɛc of the shrinking parameter ɛ for which solution exists, and its value is dependent on the value of M, and dual solutions exist for some range of values of the shrinking parameter ɛ.
Global Optimization Techniques for Fluid Flow and Propulsion Devices
NASA Technical Reports Server (NTRS)
Shyy, Wei; Papila, Nilay; Vaidyanathan, Raj; Tucker, Kevin; Griffin, Lisa; Dorney, Dan; Huber, Frank; Tran, Ken; Turner, James E. (Technical Monitor)
2001-01-01
This viewgraph presentation gives an overview of global optimization techniques for fluid flow and propulsion devices. Details are given on the need, characteristics, and techniques for global optimization. The techniques include response surface methodology (RSM), neural networks and back-propagation neural networks, design of experiments, face centered composite design (FCCD), orthogonal arrays, outlier analysis, and design optimization.
Active current sheets and candidate hot flow anomalies upstream of Mercury's bow shock
NASA Astrophysics Data System (ADS)
Uritsky, V. M.; Slavin, J. A.; Boardsen, S. A.; Sundberg, T.; Raines, J. M.; Gershman, D. J.; Collinson, G.; Sibeck, D.; Khazanov, G. V.; Anderson, B. J.; Korth, H.
2014-02-01
Hot flow anomalies (HFAs) represent a subset of solar wind discontinuities interacting with collisionless bow shocks. They are typically formed when the normal component of the motional (convective) electric field points toward the embedded current sheet on at least one of its sides. The core region of an HFA contains hot and highly deflected ion flows and rather low and turbulent magnetic field. In this paper, we report observations of possible HFA-like events at Mercury identified over a course of two planetary years. Using data from the orbital phase of the MESSENGER mission, we identify a representative ensemble of active current sheets magnetically connected to Mercury's bow shock. We show that some of these events exhibit magnetic and particle signatures of HFAs similar to those observed at other planets, and present their key physical characteristics. Our analysis suggests that Mercury's bow shock does not only mediate the flow of supersonic solar wind plasma but also provides conditions for local particle acceleration and heating as predicted by previous numerical simulations. Together with earlier observations of HFA activity at Earth, Venus, Mars, and Saturn, our results confirm that hot flow anomalies could be a common property of planetary bow shocks and show that the characteristic size of these events is controlled by the bow shock standoff distance and/or local solar wind conditions.
Compressible turbulence with slow-mode waves observed in the bursty bulk flow of plasma sheet
NASA Astrophysics Data System (ADS)
Wang, Tieyan; Cao, Jinbin; Fu, Huishan; Meng, Xuejie; Dunlop, M.
2016-03-01
In this paper, we report the evidence of compressible turbulence with slow-mode waves in a bursty bulk flow of plasma sheet. This compressible turbulence is characterized by a multiscale (1-60 s) anticorrelation between plasma density and magnetic field strength. Besides, the magnetic compressibility spectrum stays nearly constant at all the measured frequencies. Furthermore, the turbulence energy distributions are anisotropic with k⊥ > k//, and the dispersion relation is consistent with slow-mode prediction. The fluctuations of density and magnetic field have similar double slope spectrum and kurtosis. These results suggest that the slow waves are involved in the intermittent turbulence cascade from MHD to ion kinetic scales, which may have significant implications for the energy transfer in the plasma sheet.
NASA Astrophysics Data System (ADS)
Ramesh, G. K.; Gireesha, B. J.; Gorla, Rama Subba Reddy
2015-08-01
The steady two-dimensional boundary layer flow of a viscous dusty fluid over a stretching sheet with the bottom surface of the sheet heated by convection from a hot fluid is considered. The governing partial differential equations are transformed into ordinary differential equations using a similarity transformation, before being solved numerically by a Runge-Kutta-Fehlberg fourth-fifth order method (RKF45 Method) with the help of MAPLE. The effects of convective Biot number, fluid particle interaction parameter, and Prandtl number on the heat transfer characteristics are discussed. It is found that the temperature of both fluid and dust phase increases with increasing Biot number. A comparative study between the previous published and present results in a limiting sense is found in an excellent agreement.
Mustafa, Meraj; Farooq, Muhammad A.; Hayat, Tasawar; Alsaedi, Ahmed
2013-01-01
This investigation is concerned with the stagnation-point flow of nanofluid past an exponentially stretching sheet. The presence of Brownian motion and thermophoretic effects yields a coupled nonlinear boundary-value problem (BVP). Similarity transformations are invoked to reduce the partial differential equations into ordinary ones. Local similarity solutions are obtained by homotopy analysis method (HAM), which enables us to investigate the effects of parameters at a fixed location above the sheet. The numerical solutions are also derived using the built-in solver bvp4c of the software MATLAB. The results indicate that temperature and the thermal boundary layer thickness appreciably increase when the Brownian motion and thermophoresis effects are strengthened. Moreover the nanoparticles volume fraction is found to increase when the thermophoretic effect intensifies. PMID:23671576
Responses of different ion species to fast plasma flows and local dipolarization in the plasma sheet
NASA Astrophysics Data System (ADS)
Ohtani, S.; Nosé, M.; Miyashita, Y.; Lui, A. T. Y.
2015-01-01
investigate the responses of different ion species (H+, He+, He++, and O+) to fast plasma flows and local dipolarization in the plasma sheet in terms of energy density. We use energetic (9-210 keV) ion composition measurements made by the Geotail satellite at r = 10~31 RE. The results are summarized as follows: (1) whereas the O+-to-H+ ratio decreases with earthward flow velocity, it increases with tailward flow velocity with steeper Vx dependence for perpendicular flows than for parallel flows; (2) for fast earthward flows, the energy density of each ion species increases without any clear preference for heavy ions; (3) for fast tailward flows, the ion energy density initially increases, then it decreases to below the preceding levels except for O+; (4) the O+-to-H+ ratio does not increase through local dipolarization irrespective of dipolarization amplitude, background Bz, X distance, and Vx; (5) in general, the H+ and He++ ions behave similarly. Result (1) can be attributed to radial transport in the presence of the earthward gradient of the background O+-to-H+ ratio. Results (2) and (4) suggest that ion energization at local dipolarization is not mass dependent in the energy range of our interest because the ions are not magnetized irrespective of species. Result (3) can be attributed to the thinning of the plasma sheet and the preferable field-aligned escape of the H+ ions on the tailward side of the reconnection site. Result (5) suggests that the solar wind is the primary source of the high-energy H+ ions.
Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet
Bons, Paul D.; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C.; Binder, Tobias; Eisen, Olaf; Jessell, Mark W.; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka
2016-01-01
The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier. PMID:27126274
Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet
NASA Astrophysics Data System (ADS)
Bons, Paul D.; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C.; Binder, Tobias; Eisen, Olaf; Jessell, Mark W.; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka
2016-04-01
The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier.
Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet.
Bons, Paul D; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C; Binder, Tobias; Eisen, Olaf; Jessell, Mark W; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka
2016-01-01
The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier. PMID:27126274
Computational Optimization of a Natural Laminar Flow Experimental Wing Glove
NASA Technical Reports Server (NTRS)
Hartshom, Fletcher
2012-01-01
Computational optimization of a natural laminar flow experimental wing glove that is mounted on a business jet is presented and discussed. The process of designing a laminar flow wing glove starts with creating a two-dimensional optimized airfoil and then lofting it into a three-dimensional wing glove section. The airfoil design process does not consider the three dimensional flow effects such as cross flow due wing sweep as well as engine and body interference. Therefore, once an initial glove geometry is created from the airfoil, the three dimensional wing glove has to be optimized to ensure that the desired extent of laminar flow is maintained over the entire glove. TRANAIR, a non-linear full potential solver with a coupled boundary layer code was used as the main tool in the design and optimization process of the three-dimensional glove shape. The optimization process uses the Class-Shape-Transformation method to perturb the geometry with geometric constraints that allow for a 2-in clearance from the main wing. The three-dimensional glove shape was optimized with the objective of having a spanwise uniform pressure distribution that matches the optimized two-dimensional pressure distribution as closely as possible. Results show that with the appropriate inputs, the optimizer is able to match the two dimensional pressure distributions practically across the entire span of the wing glove. This allows for the experiment to have a much higher probability of having a large extent of natural laminar flow in flight.
Gupta, Diksha; Singh, Bani
2014-01-01
The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements. PMID:24672310
Gupta, Diksha; Kumar, Lokendra; Singh, Bani
2014-01-01
The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements. PMID:24672310
Stagnation-point flow and heat transfer over an exponentially shrinking sheet: A stability analysis
NASA Astrophysics Data System (ADS)
Ismail, Nurul Syuhada; Arifin, Norihan Md.; Bachok, Norfifah; Mahiddin, Norhasimah
2016-06-01
Numerical solutions for the stagnation-point flow and heat transfer over an exponentially shrinking sheet have been investigated. The governing boundary layer equations are transformed into an ordinary differential equation using a non-similar transformation. By using the bvp4c solver in MATLAB, the results of the equations can be solved numerically. Numerical results indicate that in certain parameter, the non-unique solutions for the velocity and the temperature do exist. A linear stability analysis shows that only one solution is linearly stable otherwise is unstable. Then, the stability analysis is performed to identify which solution is stable between the two non-unique solutions.
MHD Flow Of Walters' Liquid B Over A Nonlinearly Stretching Sheet
NASA Astrophysics Data System (ADS)
Siddheshwar, P. G.; Mahabaleshwar, U. S.; Chan, A.
2015-08-01
The paper discusses the boundary layer flow of a weak electrically conducting viscoelastic Walters' liquid B over a nonlinearly stretching sheet subjected to an applied transverse magnetic field, when the liquid far away from the surface is at rest. The stretching is assumed to be a quadratic function of the coordinate along the direction of stretching. An analytical expression is obtained for the stream function and velocity components as a function of the viscoelastic parameter, the Chandrasekhar number and stretching related parameters. The results have possible technological applications in liquid based systems involving stretchable materials.
Mixed convection flow of MHD Eyring-Powell nanofluid over a stretching sheet: A numerical study
NASA Astrophysics Data System (ADS)
Malik, M. Y.; Khan, Imad; Hussain, Arif; Salahuddin, T.
2015-11-01
In the present analysis incompressible two dimensional mixed convection flow of MHD Eyring-Powell nanofluid over a stretching sheet is investigated numerically. The governing highly nonlinear partial differential equations are converted into ordinary differential equations by using a similarity approach. Numerical solutions of the nonlinear ordinary differential equations are found by using a shooting method. Effects of various parameters are displayed graphically for velocity, temperature and concentration profiles. Also quantities of practical interest i.e skin friction coefficient, Nusselt number and Sherwood number are presented graphically and tabularly.
Flow and heat transfer of a nanofluid over a hyperbolically stretching sheet
NASA Astrophysics Data System (ADS)
A., Ahmad; Asghar, S.; Alsaedi, A.
2014-07-01
This article explores the boundary layer flow and heat transfer of a viscous nanofluid bounded by a hyperbolically stretching sheet. Effects of Brownian and thermophoretic diffusions on heat transfer and concentration of nanoparticles are given due attention. The resulting nonlinear problems are computed for analytic and numerical solutions. The effects of Brownian motion and thermophoretic property are found to increase the temperature of the medium and reduce the heat transfer rate. The thermophoretic property thus enriches the concentration while the Brownian motion reduces the concentration of the nanoparticles in the fluid. Opposite effects of these properties are observed on the Sherwood number.
Munir, Asif; Shahzad, Azeem; Khan, Masood
2014-01-01
The major focus of this article is to analyze the forced convective heat transfer in a steady boundary layer flow of Sisko fluid over a nonlinear stretching sheet. Two cases are studied, namely (i) the sheet with variable temperature (PST case) and (ii) the sheet with variable heat flux (PHF case). The heat transfer aspects are investigated for both integer and non-integer values of the power-law index. The governing partial differential equations are reduced to a system of nonlinear ordinary differential equations using appropriate similarity variables and solved numerically. The numerical results are obtained by the shooting method using adaptive Runge Kutta method with Broyden's method in the domain[Formula: see text]. The numerical results for the temperature field are found to be strongly dependent upon the power-law index, stretching parameter, wall temperature parameter, material parameter of the Sisko fluid and Prandtl number. In addition, the local Nusselt number versus wall temperature parameter is also graphed and tabulated for different values of pertaining parameters. Further, numerical results are validated by comparison with exact solutions as well as previously published results in the literature. PMID:24949738
The Effect of Electric Current and Strain Rate on Serrated Flow of Sheet Aluminum Alloy 5754
NASA Astrophysics Data System (ADS)
Zhao, Kunmin; Fan, Rong; Wang, Limin
2016-03-01
Electrically assisted tensile tests are carried out on sheet aluminum alloy AA5754 at electric current densities ranging from 0 to 30.4 A/mm2 and strain rates ranging from 10-3 to 10-1 s-1. The strain rate sensitivity and the serrated flow behavior are investigated in accordance with dynamic strain aging mechanism. The strain rate sensitivity changes from negative to positive and keeps increasing with current density. The tendency toward serrated flow is characterized by the onset of Portevin-Le Chatelier (PLC) instabilities, which are influenced by strain rate, temperature, and electric current. The evolutions of three types of serrated flow are observed and analyzed with respect to strain rate and current density. The magnitude of serration varies with strain rate and current density. The serrated flow can be suppressed by a high strain rate, a high temperature, or a strong electric current. The threshold values of these parameters are determined and discussed. Conventional oven-heated tensile tests are conducted to distinguish the electroplasticity. The flow stress reduces more in electrically assisted tension compared to oven-heated tension at the same temperature level. The electric current helps suppress the serrated flow at the similar temperature level of oven-heating.
The Extent of Channelized Basal Water Flow Under the Greenland Ice Sheet
NASA Astrophysics Data System (ADS)
Downs, J.; Johnson, J. V.; Harper, J. T.
2015-12-01
Glacial ice flows due to a combination of deformation and basal sliding, with sliding accounting for most of the fastest ice flow. Basal sliding is controlled by the transport of water at the glacier's bed, which can be accomplished through both high pressure, low discharge, distributed flow, or low pressure, high discharge, channelized flow. Higher pressures are generally associated with more complete decoupling of a glacier from its bed and faster flow. As the intensity of summer melt in Greenland has increased, our poor understanding of the drainage network's discharge capacity and its coupling to sliding has generated fundamental questions, such as: will larger fluxes of liquid water promote or inhibit basal sliding? To investigate this question we have implemented a model of distributed and channelized flow developed by Werder et. al 2013. The sensitivity of the modeled channel network to basal and surface geometry, melt rate, boundary conditions, and other parameters is examined in a sequence of experiments using synthetic geometries. Expanding on these experiments, we run the model with realistic surface and bedrock data from Issunguata Sermia in Western Central Greenland. These experiments benefit from a wealth of in-situ data, including observations of basal water pressure. Our results suggest that the development of large channels is limited to the margins of the ice sheet, and that higher pressures continue to prevail in the interior.
Mineral and chemical variations within an ash-flow sheet from Aso caldera, Southwestern Japan
Lipman, P.W.
1967-01-01
Although products of individual volcanic eruptions, especially voluminous ash-flow eruptions, have been considered among the best available samples of natural magmas, detailed petrographic and chemical study indicates that bulk compositions of unaltered Pleistocene ash-flow tuffs from Aso caldera, Japan, deviate significantly from original magmatic compositions. The last major ash-flow sheet from Aso caldera is as much as 150 meters thick and shows a general vertical compositional change from phenocryst-poor rhyodacite upward into phenocryst-rich trachyandesite; this change apparently reflects in inverse order a compositionally zoned magma chamber in which more silicic magma overlay more mafic magma. Details of these magmatic variations were obscured, however, by: (1) mixing of compositionally distinct batches of magma during upwelling in the vent, as indicated by layering and other heterogeneities within single pumice lumps; (2) mixing of particulate fragments-pumice lumps, ash, and phenocrysts-of varied compositions during emplacement, with the result that separate pumice lenses from a single small outcrop may have a compositional range nearly as great as the bulk-rook variation of the entire sheet; (3) density sorting of phenocrysts and ash during eruption and emplacement, resulting in systematic modal variations with distance from the caldera; (4) addition of xenocrysts, resulting in significant contamination and modification of proportions of crystals in the tuffs; and (5) ground-water leaching of glassy fractions during hydration after cooling. Similar complexities characterize ash-flow tuffs under study in southwestern Nevada and in the San Juan Mountains, Colorado, and probably are widespread in other ash-flow fields as well. Caution and careful planning are required in study of the magmatic chemistry and phenocryst mineralogy of these rocks. ?? 1967 Springer-Verlag.
A flow path model for regional water distribution optimization
NASA Astrophysics Data System (ADS)
Cheng, Wei-Chen; Hsu, Nien-Sheng; Cheng, Wen-Ming; Yeh, William W.-G.
2009-09-01
We develop a flow path model for the optimization of a regional water distribution system. The model simultaneously describes a water distribution system in two parts: (1) the water delivery relationship between suppliers and receivers and (2) the physical water delivery network. In the first part, the model considers waters from different suppliers as multiple commodities. This helps the model clearly describe water deliveries by identifying the relationship between suppliers and receivers. The physical part characterizes a physical water distribution network by all possible flow paths. The flow path model can be used to optimize not only the suppliers to each receiver but also their associated flow paths for supplying water. This characteristic leads to the optimum solution that contains the optimal scheduling results and detailed information concerning water distribution in the physical system. That is, the water rights owner, water quantity, water location, and associated flow path of each delivery action are represented explicitly in the results rather than merely as an optimized total flow quantity in each arc of a distribution network. We first verify the proposed methodology on a hypothetical water distribution system. Then we apply the methodology to the water distribution system associated with the Tou-Qian River basin in northern Taiwan. The results show that the flow path model can be used to optimize the quantity of each water delivery, the associated flow path, and the water trade and transfer strategy.
Optimization neural network for solving flow problems.
Perfetti, R
1995-01-01
This paper describes a neural network for solving flow problems, which are of interest in many areas of application as in fuel, hydro, and electric power scheduling. The neural network consist of two layers: a hidden layer and an output layer. The hidden units correspond to the nodes of the flow graph. The output units represent the branch variables. The network has a linear order of complexity, it is easily programmable, and it is suited for analog very large scale integration (VLSI) realization. The functionality of the proposed network is illustrated by a simulation example concerning the maximal flow problem. PMID:18263420
Profile Optimization Method for Robust Airfoil Shape Optimization in Viscous Flow
NASA Technical Reports Server (NTRS)
Li, Wu
2003-01-01
Simulation results obtained by using FUN2D for robust airfoil shape optimization in transonic viscous flow are included to show the potential of the profile optimization method for generating fairly smooth optimal airfoils with no off-design performance degradation.
Optimal feedback control of turbulent channel flow
NASA Technical Reports Server (NTRS)
Bewley, Thomas; Choi, Haecheon; Temam, Roger; Moin, Parviz
1993-01-01
Feedback control equations were developed and tested for computing wall normal control velocities to control turbulent flow in a channel with the objective of reducing drag. The technique used is the minimization of a 'cost functional' which is constructed to represent some balance of the drag integrated over the wall and the net control effort. A distribution of wall velocities is found which minimizes this cost functional some time shortly in the future based on current observations of the flow near the wall. Preliminary direct numerical simulations of the scheme applied to turbulent channel flow indicates it provides approximately 17 percent drag reduction. The mechanism apparent when the scheme is applied to a simplified flow situation is also discussed.
Convective heat transfer and MHD effects on Casson nanofluid flow over a shrinking sheet
NASA Astrophysics Data System (ADS)
Haq, Rizwan; Nadeem, Sohail; Khan, Zafar; Okedayo, Toyin
2014-12-01
Current study examines the magnetohydrodynamic (MHD) boundary layer flow of a Casson nanofluid over an exponentially permeable shrinking sheet with convective boundary condition. Moreover, we have considered the suction/injection effects on the wall. By applying the appropriate transformations, system of non-linear partial differential equation along with the boundary conditions are transformed to couple non-linear ordinary differential equations. The resulting systems of non-linear ordinary differential equations are solved numerically using Runge-Kutta method. Numerical results for velocity, temperature and nanoparticle volume concentration are presented through graphs for various values of dimensionless parameters. Effects of parameters for heat transfer at wall and nanoparticle volume concentration are also presented through graphs and tables. At the end, fluid flow behavior is examined through stream lines. Concluding remarks are provided for the whole analysis.
Flow Past a Permeable Stretching/Shrinking Sheet in a Nanofluid Using Two-Phase Model
Zaimi, Khairy; Ishak, Anuar; Pop, Ioan
2014-01-01
The steady two-dimensional flow and heat transfer over a stretching/shrinking sheet in a nanofluid is investigated using Buongiorno’s nanofluid model. Different from the previously published papers, in the present study we consider the case when the nanofluid particle fraction on the boundary is passively rather than actively controlled, which make the model more physically realistic. The governing partial differential equations are transformed into nonlinear ordinary differential equations by a similarity transformation, before being solved numerically by a shooting method. The effects of some governing parameters on the fluid flow and heat transfer characteristics are graphically presented and discussed. Dual solutions are found to exist in a certain range of the suction and stretching/shrinking parameters. Results also indicate that both the skin friction coefficient and the local Nusselt number increase with increasing values of the suction parameter. PMID:25365118
Inflation rates, rifts, and bands in a pāhoehoe sheet flow
Hoblitt, Richard P.; Orr, Tim R.; Heliker, Christina; Denlinger, Roger P.; Hon, Ken; Cervelli, Peter F.
2012-01-01
The margins of sheet flows—pāhoehoe lavas emplaced on surfaces sloping Inflation and rift-band formation is probably cyclic, because the pattern we observed suggests episodic or crude cyclic behavior. Furthermore, some inflation rifts contain numerous bands whose spacing and general appearances are remarkably similar. We propose a conceptual model wherein the inferred cyclicity is due to the competition between the fluid pressure in the flow's liquid core and the tensile strength of the viscoelastic layer where it is weakest—in inflation rifts. The viscoelastic layer consists of lava that has cooled to temperatures between 800 and 1070 °C. This layer is the key parameter in our model because, in its absence, rift banding and stepwise changes in the flow height would not occur.
Thermal radiation and slip effects on MHD stagnation point flow of nanofluid over a stretching sheet
NASA Astrophysics Data System (ADS)
Ul Haq, Rizwan; Nadeem, Sohail; Hayat Khan, Zafar; Sher Akbar, Noreen
2015-01-01
Present model is devoted for the stagnation point flow of nanofluid with magneto-hydrodynamics (MHD) and thermal radiation effects passed over a stretching sheet. Moreover, we have considered the combined effects of velocity and thermal slip. Condition of zero normal flux of nanoparticles at the wall for the stretched flow phenomena is yet to be explored in the literature. Convinced partial differential equations of the model are transformed into the system of coupled nonlinear differential equations and then solved numerically. Graphical results are plotted for velocity, temperature and nanoparticle concentration for various values of emerging parameters. Variation of stream lines, skin friction coefficient, local Nusselt and Sherwood number are displayed along with the effective parameters. Final conclusion has been drawn on the basis of both numerical and graphs results.
Flow past a permeable stretching/shrinking sheet in a nanofluid using two-phase model.
Zaimi, Khairy; Ishak, Anuar; Pop, Ioan
2014-01-01
The steady two-dimensional flow and heat transfer over a stretching/shrinking sheet in a nanofluid is investigated using Buongiorno's nanofluid model. Different from the previously published papers, in the present study we consider the case when the nanofluid particle fraction on the boundary is passively rather than actively controlled, which make the model more physically realistic. The governing partial differential equations are transformed into nonlinear ordinary differential equations by a similarity transformation, before being solved numerically by a shooting method. The effects of some governing parameters on the fluid flow and heat transfer characteristics are graphically presented and discussed. Dual solutions are found to exist in a certain range of the suction and stretching/shrinking parameters. Results also indicate that both the skin friction coefficient and the local Nusselt number increase with increasing values of the suction parameter. PMID:25365118
Optimization of Airfoil Design for Flow Control with Plasma Actuators
NASA Astrophysics Data System (ADS)
Williams, Theodore; Corke, Thomas; Cooney, John
2011-11-01
Using computer simulations and design optimization methods, this research examines the implementation of active flow control devices on wind turbine blades. Through modifications to blade geometry in order to maximize the effectiveness of flow control devices, increases in aerodynamic performance and control of aerodynamic performance are expected. Due to this compliant flow, an increase in the power output of wind turbines is able to be realized with minimal modification and investment to existing turbine blades. This is achieved through dynamic lift control via virtual camber control. Methods using strategic flow separation near the trailing edge are analyzed to obtain desired aerodynamic performance. FLUENT is used to determine the aerodynamic performance of potential turbine blade design, and the post-processing uses optimization techniques to determine an optimal blade geometry and plasma actuator operating parameters. This work motivates the research and development of novel blade designs with flow control devices that will be tested at Notre Dame's Laboratory for Enhanced Wind Energy Design.
Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations
NASA Astrophysics Data System (ADS)
Arthern, Robert J.; Hindmarsh, Richard C. A.; Williams, C. Rosie
2015-07-01
Accurate dynamical models of the Antarctic ice sheet with carefully specified initial conditions and well-calibrated rheological parameters are needed to forecast global sea level. By adapting an inverse method previously used in electric impedance tomography, we infer present-day flow speeds within the ice sheet. This inversion uses satellite observations of surface velocity, snow accumulation rate, and rate of change of surface elevation to estimate the basal drag coefficient and an ice stiffness parameter that influences viscosity. We represent interior ice motion using a vertically integrated approximation to incompressible Stokes flow. This model represents vertical shearing within the ice and membrane stresses caused by horizontal stretching and shearing. Combining observations and model, we recover marked geographical variations in the basal drag coefficient. Relative changes in basal shear stress are smaller. No simple sliding law adequately represents basal shear stress as a function of sliding speed. Low basal shear stress predominates in central East Antarctica, where thick insulating ice allows liquid water at the base to lubricate sliding. Higher shear stress occurs in coastal East Antarctica, where a frozen bed is more likely. Examining Thwaites glacier in more detail shows that the slowest sliding often coincides with elevated basal topography. Differences between our results and a similar adjoint-based inversion suggest that inversion or regularization methods can influence recovered parameters for slow sliding and finer scales; on broader scales we recover a similar pattern of low basal drag underneath major ice streams and extensive regions in East Antarctica that move by basal sliding.
Hamid, Rohana Abdul; Nazar, Roslinda; Pop, Ioan
2015-01-01
The paper deals with a stagnation-point boundary layer flow towards a permeable stretching/shrinking sheet in a nanofluid where the flow and the sheet are not aligned. We used the Buongiorno model that is based on the Brownian diffusion and thermophoresis to describe the nanofluid in this problem. The main purpose of the present paper is to examine whether the non-alignment function has the effect on the problem considered when the fluid suction and injection are imposed. It is interesting to note that the non-alignment function can ruin the symmetry of the flows and prominent in the shrinking sheet. The fluid suction will reduce the impact of the non-alignment function of the stagnation flow and the stretching/shrinking sheet but at the same time increasing the velocity profiles and the shear stress at the surface. Furthermore, the effects of the pertinent parameters such as the Brownian motion, thermophoresis, Lewis number and the suction/injection on the flow and heat transfer characteristics are also taken into consideration. The numerical results are shown in the tables and the figures. It is worth mentioning that dual solutions are found to exist for the shrinking sheet. PMID:26440761
Fully localised nonlinear energy growth optimals in pipe flow
Pringle, Chris C. T.; Willis, Ashley P.; Kerswell, Rich R.
2015-06-15
A new, fully localised, energy growth optimal is found over large times and in long pipe domains at a given mass flow rate. This optimal emerges at a threshold disturbance energy below which a nonlinear version of the known (streamwise-independent) linear optimal [P. J. Schmid and D. S. Henningson, “Optimal energy density growth in Hagen-Poiseuille flow,” J. Fluid Mech. 277, 192–225 (1994)] is selected and appears to remain the optimal up until the critical energy at which transition is triggered. The form of this optimal is similar to that found in short pipes [Pringle et al., “Minimal seeds for shear flow turbulence: Using nonlinear transient growth to touch the edge of chaos,” J. Fluid Mech. 702, 415–443 (2012)], but now with full localisation in the streamwise direction. This fully localised optimal perturbation represents the best approximation yet of the minimal seed (the smallest perturbation which is arbitrarily close to states capable of triggering a turbulent episode) for “real” (laboratory) pipe flows. Dependence of the optimal with respect to several parameters has been computed and establishes that the structure is robust.
Fully localised nonlinear energy growth optimals in pipe flow
NASA Astrophysics Data System (ADS)
Pringle, Chris C. T.; Willis, Ashley P.; Kerswell, Rich R.
2015-06-01
A new, fully localised, energy growth optimal is found over large times and in long pipe domains at a given mass flow rate. This optimal emerges at a threshold disturbance energy below which a nonlinear version of the known (streamwise-independent) linear optimal [P. J. Schmid and D. S. Henningson, "Optimal energy density growth in Hagen-Poiseuille flow," J. Fluid Mech. 277, 192-225 (1994)] is selected and appears to remain the optimal up until the critical energy at which transition is triggered. The form of this optimal is similar to that found in short pipes [Pringle et al., "Minimal seeds for shear flow turbulence: Using nonlinear transient growth to touch the edge of chaos," J. Fluid Mech. 702, 415-443 (2012)], but now with full localisation in the streamwise direction. This fully localised optimal perturbation represents the best approximation yet of the minimal seed (the smallest perturbation which is arbitrarily close to states capable of triggering a turbulent episode) for "real" (laboratory) pipe flows. Dependence of the optimal with respect to several parameters has been computed and establishes that the structure is robust.
Overexcitability and Optimal Flow in Talented Dancers, Singers, and Athletes
ERIC Educational Resources Information Center
Thomson, Paula; Jaque, S. Victoria
2016-01-01
Overexcitability (OE) and optimal flow are variables shared by talented individuals. This study demonstrated that the dancer (n = 86) and opera singer (n = 61) groups shared higher OE profiles compared to the athlete group (n = 50). Two self-report instruments assessed flow (global and subscales) and the five OE dimensions. All groups endorsed…
Optimization of laser welding of DP/TRIP steel sheets using statistical approach
NASA Astrophysics Data System (ADS)
Reisgen, U.; Schleser, M.; Mokrov, O.; Ahmed, E.
2012-02-01
Generally, the quality of a weld joint is directly influenced by the welding input parameter settings. Selection of proper process parameters is important to obtain the desired weld bead profile and quality. In this research work, numerical and graphical optimization techniques of the CO 2 laser beam welding of dual phase (DP600)/transformation induced plasticity (TRIP700) steel sheets were carried out using response surface methodology (RSM) based on Box-Behnken design. The procedure was established to improve the weld quality, increase the productivity and minimize the total operation cost by considering the welding parameters range of laser power (2-2.2 kW), welding speed (40-50 mm/s) and focus position (-1 to 0 mm). It was found that, RSM can be considered as a powerful tool in experimental welding optimization, even when the experimenter does not have a model for the process. Strong, efficient and low cost weld joints could be achieved using the optimum welding conditions.
Optimized profiles for incompressible flow metering nozzles
NASA Astrophysics Data System (ADS)
Lakshminarayanan, R.; Haji-Sheikh, A.; Lou, D. Y. S.; Spindler, M.
1988-04-01
The Euler-Lagrange equation was used to minimize shear stress in designing a flow-metering nozzle. The flow field in the nozzle was computed by solving the momentum equation in integral form. The profile of the nozzle was obtained by minimizing the shear losses in the converging section of the nozzle. Following computation of the profile, a metering nozzle was designed, constructed, and subsequently tested to evaluate the validity of the analysis. The nozzle was designed for a pipe diameter of 15.24 cm (6 in.) and a throat diameter of 9.266 cm (3.648 in.). The test results indicated a marked increase in the value of the discharge coefficient when it is compared with that for the ASME standard nozzle. The computed pressure distribution is in good agreement with the experimental data.
NASA Astrophysics Data System (ADS)
Nadeem, S.; Hussain, Anwar; Khan, Majid
2010-03-01
In the present study, we have described the stagnation point flow of a viscous fluid towards a stretching sheet. The complete analytical solution of the boundary layer equation has been obtained by homotopy analysis method (HAM). The solutions are compared with the available numerical results obtained by Nazar et al. [Nazar R, Amin N, Filip D, Pop I. Unsteady boundary layer flow in the region of the stagnation point on a stretching sheet. Int J Eng Sci 2004;42:1241-53] and a good agreement is found. The convergence region is also computed which shows the validity of the HAM solution.
Flow sheet development for the dissolution of unirradiated Mark 42 fuel tubes in F-Canyon, Part II
Murray, A.M.
1999-09-20
Two dissolution flow sheets were tested for the desorption of unirradiated Mark 42 fuel tubes. Both the aluminum (from the can, cladding, and fuel core) and the plutonium oxide (PuO{sub 2}) are dissolved simultaneously, i.e., a co-dissolution flow sheet. In the first series of tests, 0.15 and 0.20 molar (M) potassium fluoride (KF) solutions were used and the dissolution extended over several days. In the other series of tests, solutions with higher concentrations of fluoride (0.25 to 0.30 M) were used. Calcium fluoride (CaF{sub 2}) was used in those tests as the fluoride source.
NASA Astrophysics Data System (ADS)
Mozumder, Chandan K.
The objective in crashworthiness design is to generate plastically deformable energy absorbing structures which can satisfy the prescribed force-displacement (FD) response. The FD behavior determines the reaction force, displacement and the internal energy that the structure should withstand. However, attempts to include this requirement in structural optimization problems remain scarce. The existing commercial optimization tools utilize models under static loading conditions because of the complexities associated with dynamic/impact loading. Due to the complexity of a crash event and the consequent time required to numerically analyze the dynamic response of the structure, classical methods (i.e., gradient-based and direct) are not well developed to solve this undertaking. This work presents an approach under the framework of the hybrid cellular automaton (HCA) method to solve the above challenge. The HCA method has been successfully applied to nonlinear transient topology optimization for crashworthiness design. In this work, the HCA algorithm has been utilized to develop an efficient methodology for synthesizing shell-based sheet metal structures with optimal material thickness distribution under a dynamic loading event using topometry optimization. This method utilizes the cellular automata (CA) computing paradigm and nonlinear transient finite element analysis (FEA) via ls-dyna. In this method, a set field variables is driven to their target states by changing a convenient set of design variables (e.g., thickness). These rules operate locally in cells within a lattice that only know local conditions. The field variables associated with the cells are driven to a setpoint to obtain the desired structure. This methodology is used to design for structures with controlled energy absorption with specified buckling zones. The peak reaction force and the maximum displacement are also constrained to meet the desired safety level according to passenger safety
Mathematical Modeling of Filtration Flows from Foundation Pits Fenced with Zhukovskii Sheet Piles
NASA Astrophysics Data System (ADS)
Bereslavskii, É. N.
2014-01-01
Consideration is given to the filtration of water from foundation pits fenced with Zhukovskii sheet piles through a ground layer underlain by a well-permeable confined aquifer on whose roof there is a water-impermeable portion. A mixed multiparametric boundary-value problem of the theory of analytical functions is formulated, which is solved with the Polubarinova-Kochina method. Based on this model, an algorithm of calculation of the filrtation characteristics is developed for situations where, in water motion from the foundation pits, one has to take into account the joint influence of such important factors, as seepage onto the free surface, upthrust from the water of the underlying highly permeable aquifer, and the presence of the impermeable inclusion on the roof of the latter, on the pattern of the phenomenon. Limiting cases of the model are considered which are related to the absence of one factor characterizing the modeled process (upthrust, an impermeable inclusion, seepage) and to the degeneration of the foundation pits into a submergence band semiinfinite on the left. A solution of the problem is given for the scheme under the assumption of a finite value of the flow velocity at the end of a sheet pile; it is a certain analog of the Zhukovskii classical problem.
Heat Transfer of Viscoelastic Fluid Flow due to Nonlinear Stretching Sheet with Internal Heat Source
NASA Astrophysics Data System (ADS)
Nandeppanavar, M. M.; Siddalingappa, M. N.; Jyoti, H.
2013-08-01
In the present paper, a viscoelastic boundary layer flow and heat transfer over an exponentially stretching continuous sheet in the presence of a heat source/sink has been examined. Loss of energy due to viscous dissipation of the non-Newtonian fluid has been taken into account in this study. Approximate analytical local similar solutions of the highly non-linear momentum equation are obtained for velocity distribution by transforming the equation into Riccati-type and then solving this sequentially. Accuracy of the zero-order analytical solutions for the stream function and velocity are verified by numerical solutions obtained by employing the Runge-Kutta fourth order method involving shooting. Similarity solutions of the temperature equation for non-isothermal boundary conditions are obtained in the form of confluent hypergeometric functions. The effect of various physical parameters on the local skin-friction coefficient and heat transfer characteristics are discussed in detail. It is seen that the rate of heat transfer from the stretching sheet to the fluid can be controlled by suitably choosing the values of the Prandtl number Pr and local Eckert number E, local viscioelastic parameter k*1 and local heat source/ sink parameter β*
Liu, H. H.
2010-09-15
Optimality principles have been used for investigating physical processes in different areas. This work attempts to apply an optimal principle (that water flow resistance is minimized on global scale) to steady-state unsaturated flow processes. Based on the calculus of variations, we show that under optimal conditions, hydraulic conductivity for steady-state unsaturated flow is proportional to a power function of the magnitude of water flux. This relationship is consistent with an intuitive expectation that for an optimal water flow system, locations where relatively large water fluxes occur should correspond to relatively small resistance (or large conductance). Similar results were also obtained for hydraulic structures in river basins and tree leaves, as reported in other studies. Consistence of this theoretical result with observed fingering-flow behavior in unsaturated soils and an existing model is also demonstrated.
Nagashima, Yoshinao; Igaki, Michihito; Suzuki, Atsushi; Tsuchiya, Shuichi; Yamazaki, Yoshimi; Hishinuma, Michiko; Oh-Ishi, Sachiko; Majima, Masataka
2011-01-01
To promote the practical application of a Japanese traditional medical treatment, such as hot compresses, we developed a plaster-type warming device consisting of a heat- and steam-generating sheet (HSG sheet). First, we tested its effects when applied to the anterior abdominal wall or lumbar region of women complaining of a tendency towards constipation. Application of the sheet to either region produced a feeling of comfort in the abdomen, as assessed by a survey of the subjects. The significant increases in the total hemoglobin observed in these regions suggested an increase in peripheral blood flow, and significant increases in the HF component on ECG and in the amplitude of gastric motility suggested parasympathetic predominance. We concluded that application of the HSG sheet improves the peripheral hemodynamics and autonomic regulation, induces a feeling of comfort in the abdomen, and provides a beneficial environment for the improvement of gastrointestinal movements. PMID:21584198
Experimental study of sheet flow regime of sediment transport in a laboratory flume.
NASA Astrophysics Data System (ADS)
Revil-Baudard, Thibaud; Chauchat, Julien; Hurther, David; Barthélémy, Eric; Michallet, Hervé; Snabre, Patrick
2014-05-01
The sheet flow regime of sediment transport occurs when the shear stress exerted by the fluid flow on the sediment bed is high enough to set in motion a thick layer of particles. This phenomenon is very important for river and coastal morphodynamical evolution. However, the key mechanisms controlling this regime such as intergranular interactions or turbulent processes in dense fluid-sediment mixture are not well understood yet. For this purpose, an original laboratory experiment has been set up at LEGI in a tilted flume (10 meters long, 35 centimeters wide). 3mm plastic (PMMA) particles are stored in a 3m long tank located close to the channel outlet. The channel is tilted at 0.5 per cent slope and the fluid flow rate is 35 l/s. The instrumentation is composed of an acoustic profiler, ACVP, a high speed camera and a water level sensor. The acoustic profiler allows to get streamwise and vertical velocities profiles from the clear water flow down to the fixed bed with great spatial and temporal resolution (3mm and 0,013s respectively) permitting a good characterization of turbulence. The high speed camera together with a videotrajectography method allow to get sediment velocity profiles and qualitative concentration profiles close to the wall. To compensate the lack of sediment recirculation and the short duration of the experiment, it is repeated to carry out ensemble averaging. The statistical protocol for the treatment of the turbulent signal is presented. This initial treatment allows the estimation of the mean velocity, the turbulent shear and the normal stresses profiles. From these profiles, reproducibility and steadiness of the flow are verified and the main mechanisms of momentum transfer acting from the fixed bed to the dilute suspension are analyzed. The mean velocity profile close to the bed shows three different regions, from bottom to top, an exponential tail, a linear layer and a logarithmic layer. The exponential tail is characteristic of a Coulomb
Mansur, Syahira; Ishak, Anuar; Pop, Ioan
2015-01-01
The magnetohydrodynamic (MHD) stagnation point flow of a nanofluid over a permeable stretching/shrinking sheet is studied. Numerical results are obtained using boundary value problem solver bvp4c in MATLAB for several values of parameters. The numerical results show that dual solutions exist for the shrinking case, while for the stretching case, the solution is unique. A stability analysis is performed to determine the stability of the dual solutions. For the stable solution, the skin friction is higher in the presence of magnetic field and increases when the suction effect is increased. It is also found that increasing the Brownian motion parameter and the thermophoresis parameter reduces the heat transfer rate at the surface. PMID:25760733
Flow and heat transfer to modified second grade fluid over a non-linear stretching sheet
NASA Astrophysics Data System (ADS)
Khan, Masood; Rahman, Masood ur
2015-08-01
The objective of the present work is to analyze the two-dimensional boundary layer flow and heat transfer of a modified second grade fluid over a non-linear stretching sheet of constant surface temperature. The modelled momentum and energy equations are deduced to a system of ordinary differential equations by employing suitable transformations in boundary layer region and integrated numerically by fourth and fifth order Runge-Kutta Fehlberg method. Additionally, the analytic solutions of the governing problem are presented for some special cases. The secured results make it clear that the power-law index reduces both the momentum and thermal boundary layers. While the incremented values of the generalized second grade parameter leads to an increase in the momentum boundary layer and a decrease in the thermal boundary layer. To see the validity of the present results we have made a comparison with the previously published results as a special case with an outstanding compatibility.
Forced convection analysis for generalized Burgers nanofluid flow over a stretching sheet
NASA Astrophysics Data System (ADS)
Khan, Masood; Khan, Waqar Azeem
2015-10-01
This article reports the two-dimensional forced convective flow of a generalized Burgers fluid over a linearly stretched sheet under the impacts of nano-sized material particles. Utilizing appropriate similarity transformations the coupled nonlinear partial differential equations are converted into a set of coupled nonlinear ordinary differential equations. The analytic results are carried out through the homotopy analysis method (HAM) to investigate the impact of various pertinent parameters for the velocity, temperature and concentration fields. The obtained results are presented in tabular form as well as graphically and discussed in detail. The presented results show that the rate of heat transfer at the wall and rate of nanoparticle volume fraction diminish with each increment of the thermophoresis parameter. While incremented values of the Brownian motion parameter lead to a quite opposite effect on the rates of heat transfer and nanoparticle volume fraction at the wall.
On magnetohydrodynamic flow of second grade nanofluid over a nonlinear stretching sheet
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Aziz, Arsalan; Muhammad, Taseer; Ahmad, Bashir
2016-06-01
This research article addresses the magnetohydrodynamic (MHD) flow of second grade nanofluid over a nonlinear stretching sheet. Heat and mass transfer aspects are investigated through the thermophoresis and Brownian motion effects. Second grade fluid is assumed electrically conducting through a non-uniform applied magnetic field. Mathematical formulation is developed subject to small magnetic Reynolds number and boundary layer assumptions. Newly constructed condition having zero mass flux of nanoparticles at the boundary is incorporated. Transformations have been invoked for the reduction of partial differential systems into the set of nonlinear ordinary differential systems. The governing nonlinear systems have been solved for local behavior. Graphical results of different influential parameters are studied and discussed in detail. Computations for skin friction coefficient and local Nusselt number have been carried out. It is observed that the effects of thermophoresis parameter on the temperature and nanoparticles concentration distributions are qualitatively similar. The temperature and nanoparticles concentration distributions are enhanced for the larger magnetic parameter.
NASA Astrophysics Data System (ADS)
Ahmad, Rida; Mustafa, M.; Hayat, T.; Alsaedi, A.
2016-06-01
Recent advancements in nanotechnology have led to the discovery of new generation coolants known as nanofluids. Nanofluids possess novel and unique characteristics which are fruitful in numerous cooling applications. Current work is undertaken to address the heat transfer in MHD three-dimensional flow of magnetic nanofluid (ferrofluid) over a bidirectional exponentially stretching sheet. The base fluid is considered as water which consists of magnetite-Fe3O4 nanoparticles. Exponentially varying surface temperature distribution is accounted. Problem formulation is presented through the Maxwell models for effective electrical conductivity and effective thermal conductivity of nanofluid. Similarity transformations give rise to a coupled non-linear differential system which is solved numerically. Appreciable growth in the convective heat transfer coefficient is observed when nanoparticle volume fraction is augmented. Temperature exponent parameter serves to enhance the heat transfer from the surface. Moreover the skin friction coefficient is directly proportional to both magnetic field strength and nanoparticle volume fraction.
Mansur, Syahira; Ishak, Anuar; Pop, Ioan
2015-01-01
The magnetohydrodynamic (MHD) stagnation point flow of a nanofluid over a permeable stretching/shrinking sheet is studied. Numerical results are obtained using boundary value problem solver bvp4c in MATLAB for several values of parameters. The numerical results show that dual solutions exist for the shrinking case, while for the stretching case, the solution is unique. A stability analysis is performed to determine the stability of the dual solutions. For the stable solution, the skin friction is higher in the presence of magnetic field and increases when the suction effect is increased. It is also found that increasing the Brownian motion parameter and the thermophoresis parameter reduces the heat transfer rate at the surface. PMID:25760733
Optimized boundary driven flows for dynamos in a sphere
Khalzov, I. V.; Brown, B. P.; Cooper, C. M.; Weisberg, D. B.; Forest, C. B.
2012-11-15
We perform numerical optimization of the axisymmetric flows in a sphere to minimize the critical magnetic Reynolds number Rm{sub cr} required for dynamo onset. The optimization is done for the class of laminar incompressible flows of von Karman type satisfying the steady-state Navier-Stokes equation. Such flows are determined by equatorially antisymmetric profiles of driving azimuthal (toroidal) velocity specified at the spherical boundary. The model is relevant to the Madison plasma dynamo experiment, whose spherical boundary is capable of differential driving of plasma in the azimuthal direction. We show that the dynamo onset in this system depends strongly on details of the driving velocity profile and the fluid Reynolds number Re. It is found that the overall lowest Rm{sub cr} Almost-Equal-To 200 is achieved at Re Almost-Equal-To 240 for the flow, which is hydrodynamically marginally stable. We also show that the optimized flows can sustain dynamos only in the range Rm{sub cr}
NASA Astrophysics Data System (ADS)
Domack, E. W.; Lavoie, C.; Scambos, T. A.; Pettit, E. C.; Schenke, H. W.; Yoo, K. C.; Larter, R. D.; Gutt, J.; Wellner, J.; Canals, M.; Anderson, J. B.; Amblas, D.
2014-12-01
We provide a new map of swath bathymetry for the northern Antarctic Peninsula, including data sets from five national programs. Our map allows for the compilation and examination of Late Glacial Maximum (LGM) paleo-ice sheet/stream flow directions developed upon the seafloor from the preservation of: mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and accumulation centers (ice domes). The results show a flow divergence in Larsen B embayment, between flow emanating off the Seal Nunataks (including Robertson Island) that directed ice in a southeast direction, then easterly as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" directed ice southeasterly then southward, as ice overflowed the Jason Peninsula to reach the Jason Trough, the southern perimeter of the embayment. This reconstruction is far more detailed than other recent compilations because we followed specific flow indicators and have kept tributary flow paths parallel. Our reconstitution also refines the extent of at least five other distinct paleo-ice stream systems which in turn serve to delineate seven broad regions where ice domes must have been centered across the continental shelf during the LGM.
The Relationship of Ion Beams and Fast Flows in the Plasma Sheet Boundary Layer
NASA Technical Reports Server (NTRS)
Parks, G. K.; Reme, H.; Lin, R. P.; Sanderson, T.; Germany, G. A.; Spann, James F., Jr.; Brittnacher, M. J.; McCarthy, M.; Chen, L. J.; Larsen, D.; Phan, T. D.
1998-01-01
We report new findings on the behavior of plasmas in the vicinity of the plasma sheet boundary layer (PSBL). A large geometrical factor detector on WIND (3D plasma experiment) has discovered a unidirectional ion beam streaming in the tailward direction missed by previous observations. This tailward beam is as intense as the earthward streaming beam and it is found just inside the outer edge of the PSBL where earthward streaming beams are observed. The region where this tailward beam is observed includes an isotropic plasma component which is absent in the outer edge where earthward streaming beams are found. When these different distributions are convolved to calculate the velocity moments, fast flows (greater than 400 km/s) result in the earthward direction and much slower flows (less than 200 km/s) in the tailward direction. These new findings are substantially different from previous observations. Thus, the interpretation of fast flows and earthward and counterstreaming ion beams in terms of a neutral line model must be reexamined.
NASA Astrophysics Data System (ADS)
Johnson, Ken I.; Smith, Mark T.; Lavender, Curt A.; Khalell, Mohammad A.
1994-10-01
Using aluminum instead of steel in transportation systems could dramatically reduce the weight of vehicles, an effective way of decreasing energy consumption and emissions. The current cost of sheet metal formed (SMF) aluminum alloys (about $4 per pound) and the relatively long forming times of current materials are serious drawbacks to the widespread use of SMF in industry. The interdependence of materials testing and model development is critical to optimizing SMF since the current process is conducted in a heated, pressurized die where direct measurement of critical SMF parameters is extremely difficult. Numerical models provide a means of tracking the forming process, allowing the applied gas pressure to be adjusted to maintain the optimum SMF behavior throughout the forming process. Thus, models can help produce the optimum SMF component in the least amount of time. The Pacific Northwest Laboratory is integrating SMF model development with research in improved aluminum alloys for SMF. The objectives of this research are: develop and characterize competitively priced aluminum alloys for SMF applications in industry; improve numerical models to accurately predict the optimum forming cycle for reduced forming time and improved quality; and verify alloy performance and model accuracy with forming tests conducted in PNL's Superplastic Forming User Facility. The activities performed in this technology maturation project represent a critical first step in achieving these objectives through cooperative research among industry, PNL, and universities.
NASA Astrophysics Data System (ADS)
Uddin, M. J.; Ferdows, M.; Bég, O. Anwar
2014-10-01
Two-dimensional magnetohydrodynamic boundary layer flow of non-Newtonian power-law nanofluids past a linearly stretching sheet with a linear hydrodynamic slip boundary condition is investigated numerically. The non-Newtonian nanofluid model incorporates the effects of Brownian motion and thermophoresis. Similarity transformations and corresponding similarity equations of the transport equations are derived via a linear group of transformations. The transformed equations are solved numerically using Runge-Kutta-Fehlberg fourth-fifth order numerical method available in the Maple 14 software for the influence of power-law (rheological) index, Lewis number, Prandtl number, thermophoresis parameter, Brownian motion parameter, magnetic field parameter and linear momentum slip parameter. Validation is achieved with an optimized Nakamura implicit finite difference algorithm (NANONAK). Representative results for the dimensionless axial velocity, temperature and concentration profiles have been presented graphically. The present results of skin friction factor and reduced heat transfer rate are also compared with the published results for several special cases of the model and found to be in close agreement. The study has applications in electromagnetic nano-materials processing.
NASA Astrophysics Data System (ADS)
Corti, Giacomo; Zeoli, Antonio
2016-04-01
The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. This effect has been tested in previous analogue models, which however applied to ice sheets grounded above sea level (e.g., East Antarctic Ice Sheet; Antarctic Peninsula and the Larsen Ice Shelf). In this work we expand these previous results by performing small-scale laboratory models that analyse the influence of ice shelf collapse on the flow of ice streams draining an ice sheet grounded below sea level (e.g., the West Antarctic Ice Sheet). The analogue models, with dimensions (width, length, thickness) of 120x70x1.5cm were performed at the Tectonic Modelling Laboratory of CNR-IGG of Florence, Italy, by using Polydimethilsyloxane (PDMS) as analogue for the flowing ice. This transparent, Newtonian silicone has been shown to well approximate the rheology of natural ice. The silicone was allowed to flow into a water reservoir simulating natural conditions in which ice streams flow into the sea, terminating in extensive ice shelves which act as a buttress for their glaciers and slow their flow. The geometric scaling ratio was 10(-5), such that 1cm in the models simulated 1km in nature; velocity of PDMS (a few mm per hour) simulated natural velocities of 100-1000 m/year. Instability of glacier flow was induced by manually removing a basal silicone platform (floating on water) exerting backstresses to the flowing analogue glacier: the simple set-up adopted in the experiments isolates the effect of the removal of the buttressing effect that the floating platform exerts on the flowing glaciers, thus offering insights into the influence of this parameter on the flow perturbations resulting from a collapse event. The experimental results showed a significant increase in glacier velocity close to its outlet following ice shelf breakup, a process similar to what
Aerodynamic optimization by simultaneously updating flow variables and design parameters
NASA Technical Reports Server (NTRS)
Rizk, M. H.
1990-01-01
The application of conventional optimization schemes to aerodynamic design problems leads to inner-outer iterative procedures that are very costly. An alternative approach is presented based on the idea of updating the flow variable iterative solutions and the design parameter iterative solutions simultaneously. Two schemes based on this idea are applied to problems of correcting wind tunnel wall interference and optimizing advanced propeller designs. The first of these schemes is applicable to a limited class of two-design-parameter problems with an equality constraint. It requires the computation of a single flow solution. The second scheme is suitable for application to general aerodynamic problems. It requires the computation of several flow solutions in parallel. In both schemes, the design parameters are updated as the iterative flow solutions evolve. Computations are performed to test the schemes' efficiency, accuracy, and sensitivity to variations in the computational parameters.
Optimal Shape Design of a Plane Diffuser in Turbulent Flow
NASA Astrophysics Data System (ADS)
Lim, Seokhyun; Choi, Haecheon
2000-11-01
Stratford (1959) experimentally designed an optimal shape of plane diffuser for maximum pressure recovery by having zero skin friction throughout the region of pressure rise. In the present study, we apply an algorithm of optimal shape design developed by Pironneau (1973, 1974) and Cabuk & Modi (1992) to a diffuser in turbulent flow, and show that maintaining zero skin friction in the pressure-rise region is an optimal condition for maximum pressure recovery at the diffuser exit. For turbulence model, we use the k-ɛ-v^2-f model by Durbin (1995) which is known to accurately predict flow with separation. Our results with this model agree well with the previous experimental and LES results for a diffuser shape tested by Obi et al. (1993). From this initial shape, an optimal diffuser shape for maximum pressure recovery is obtained through an iterative procedure. The optimal diffuser has indeed zero skin friction throughout the pressure-rise region, and thus there is no separation in the flow. For the optimal diffuser shape obtained, an LES is being conducted to investigate the turbulence characteristics near the zero-skin-friction wall. A preliminary result of LES will also be presented.
Reorganization of ice sheet flow patterns in Arctic Canada and the mid-Pleistocene transition
NASA Astrophysics Data System (ADS)
Refsnider, Kurt A.; Miller, Gifford H.
2010-07-01
Evidence for the evolution of Laurentide Ice Sheet (LIS) basal thermal regime patterns during successive glaciations is poorly preserved in the geologic record. Here we explore a new approach to constrain the distribution of cold-based ice across central Baffin Island in the eastern Canadian Arctic over many glacial-interglacial cycles by combining till geochemistry and cosmogenic radionuclide (CRN) data. Parts of the landscaped with geomorphic evidence for limited glacial erosion are covered by till characterized by high chemical index of alteration (CIA) values and CRN concentrations requiring complicated burial-exposure histories. Till from regions scoured by glacial erosion have CIA values indistinguishable from local bedrock and CRN concentrations that can be explained by simple exposure following deglaciation. CRN modeling results based on these constraints suggest that the weathered tills were deposited by 1.9 to 1.2 Ma, and by that time the fiorded Baffin Island coastline must have developed close to its modern configuration as piracy of ice flow by the most efficient fiord systems resulted in a major shift in the basal thermal regime across the northeastern LIS. The resultant concentration of ice flow in fewer outlet systems may help explain the cause of the mid-Pleistocene transition from 41- to 100-kyr glacial cycles.
NASA Astrophysics Data System (ADS)
Viparelli, E.; Hernandez Moreira, R. R.; Blom, A.
2015-12-01
A perusal of the literature on bedload transport revealed that, notwithstanding the large number of studies on bedform morphology performed in the past decades, the upper plane bed regime has not been thoroughly investigated and the distinction between the upper plane bed and sheet flow transport regimes is still poorly defined. Previous experimental work demonstrated that the upper plane bed regime is characterized by long wavelength and small amplitude bedforms that migrate downstream. These bedforms, however, were not observed in experiments on sheet flow transport suggesting that the upper plane bed and the sheet flow are two different regimes. We thus designed and performed experiments in a sediment feed flume in the hydraulic laboratory of the Department of Civil and Environmental Engineering at the University of South Carolina at Columbia to study the transition from upper plane bed to sheet flow regime. Periodic measurements of water surface and bed elevation, bedform geometry and thicknesses of the bedload layer were performed by eyes, and with cameras, movies and a system of six ultrasonic probes that record the variations of bed elevation at a point over time. We used the time series of bed elevations to determine the probability functions of bed elevation. These probability functions are implemented in a continuous model of river morphodynamics, i.e. a model that does not use the active layer approximation to describe the sediment fluxes between the bedload and the deposit and that should thus be able to capture the details of the vertical and streamwise variation of the deposit grain size distribution. This model is validated against the experimental results for the case of uniform material. We then use the validated model in the attempt to study if and how the spatial distribution of grain sizes in the deposit changes from upper plane bed regime to sheet flow and if these results are influenced by the imposed rates of base level rise.
Optimal active power dispatch by network flow approach
Carvalho, M.F. ); Soares, S.; Ohishi, T. )
1988-11-01
In this paper the optimal active power dispatch problem is formulated as a nonlinear capacitated network flow problem with additional linear constraints. Transmission flow limits and both Kirchhoff's laws are taken into account. The problem is solved by a Generalized Upper Bounding technique that takes advantage of the network flow structure of the problem. The new approach has potential applications on power systems problems such as economic dispatch, load supplying capability, minimum load shedding, and generation-transmission reliability. The paper also reviews the use of transportation models for power system analysis. A detailed illustrative example is presented.
Fault-related fluid flow, Beech Mountain thrust sheet, Blue Ridge Province, Tennessee-North Carolina
Waggoner, W.K.; Mora, C.I. . Dept. of Geological Sciences)
1992-01-01
The latest proterozoic Beech Granite is contained within the Beech Mountain thrust sheet (BMTS), part of a middle-late Paleozoic thrust complex located between Mountain City and Grandfather Mountain windows in the western Blue Ridge of TN-NC. At the base of the BMTS, Beech Granite is juxtaposed against lower Paleozoic carbonate and elastics of the Rome Fm. along the Stone Mountain thrust on the southeaster margin of the Mountain City window. At the top of the BMTS, Beech Granite occurs adjacent to Precambrian mafic rocks of the Pumpkin Patch thrust sheet (PPTS). The Beech Granite is foliated throughout the BMTS with mylonitization and localized cataclasis occurring within thrust zones along the upper and lower margins of the BMTS. Although the degree of mylonitization and cataclasis increases towards the thrusts, blocks of relatively undeformed granite also occur within these fault zones. Mylonites and thrusts are recognized as conduits for fluid movement, but the origin of the fluids and magnitude and effects of fluid migration are not well constrained. This study was undertaken to characterize fluid-rock interaction within the Beech Granite and BMTS. Extensive mobility of some elements/compounds within the thrust zones, and the isotopic and mineralogical differences between the thrust zones and interior of the BMTS indicate that fluid flow was focused within the thrust zones. The wide range of elevated temperatures (400--710 C) indicated by qz-fsp fractionations suggest isotopic disequilibrium. Using a more likely temperature range of 300--400 C for Alleghanian deformation, calculated fluid compositions indicate interactions with a mixture of meteoric-hydrothermal and metamorphic water with delta O-18 = 2.6--7.5[per thousand] for the upper thrust zone and 1.3 to 6.2[per thousand] for the lower thrust zone. These ranges are similar to isotopic data reported for other Blue Ridge thrusts and may represent later periods of meteoric water influx.
NASA Astrophysics Data System (ADS)
Winter, Kate; Woodward, John; Ross, Neil; Dunning, Stuart A.; Bingham, Robert G.; Corr, Hugh F. J.; Siegert, Martin J.
2015-09-01
Despite the importance of ice streaming to the evaluation of West Antarctic Ice Sheet (WAIS) stability we know little about mid- to long-term dynamic changes within the Institute Ice Stream (IIS) catchment. Here we use airborne radio echo sounding to investigate the subglacial topography, internal stratigraphy, and Holocene flow regime of the upper IIS catchment near the Ellsworth Mountains. Internal layer buckling within three discrete, topographically confined tributaries, through Ellsworth, Independence, and Horseshoe Valley Troughs, provides evidence for former enhanced ice sheet flow. We suggest that enhanced ice flow through Independence and Ellsworth Troughs, during the mid-Holocene to late Holocene, was the source of ice streaming over the region now occupied by the slow-flowing Bungenstock Ice Rise. Although buckled layers also exist within the slow-flowing ice of Horseshoe Valley Trough, a thicker sequence of surface-conformable layers in the upper ice column suggests slowdown more than ~4000 years ago, so we do not attribute enhanced flow switch-off here, to the late Holocene ice-flow reorganization. Intensely buckled englacial layers within Horseshoe Valley and Independence Troughs cannot be accounted for under present-day flow speeds. The dynamic nature of ice flow in IIS and its tributaries suggests that recent ice stream switching and mass changes in the Siple Coast and Amundsen Sea sectors are not unique to these sectors, that they may have been regular during the Holocene and may characterize the decline of the WAIS.
Optimization of an Extrusion Die for Polymer Flow
NASA Astrophysics Data System (ADS)
Ridene, Y. Chahbani; Graebling, D.; Boujelbene, M.
2011-01-01
In this work, we used the CFD software PolyFlow to optimize the extrusion process of polystyrene flow. In this process, the flow of the molten polymer through the die can be viewed as a critical step for the material in terms of shear rate, self heating by viscous dissipation and temperature reached. The simulation is focused on the flow and heat transfer in the die to obtain a uniform velocity profile and a uniform temperature profile. The rheological behavior of polymer melt was described by the nonlinear Giesekus model. The dependence of the viscosity has also to be taken into account for a correct description of the flow. The design of the die has been validated by our numerical simulation.
Khan, Junaid Ahmad; Mustafa, M.; Hayat, T.; Sheikholeslami, M.; Alsaedi, A.
2015-01-01
This work deals with the three-dimensional flow of nanofluid over a bi-directional exponentially stretching sheet. The effects of Brownian motion and thermophoretic diffusion of nanoparticles are considered in the mathematical model. The temperature and nanoparticle volume fraction at the sheet are also distributed exponentially. Local similarity solutions are obtained by an implicit finite difference scheme known as Keller-box method. The results are compared with the existing studies in some limiting cases and found in good agreement. The results reveal the existence of interesting Sparrow-Gregg-type hills for temperature distribution corresponding to some range of parametric values. PMID:25785857
Khan, Junaid Ahmad; Mustafa, M; Hayat, T; Sheikholeslami, M; Alsaedi, A
2015-01-01
This work deals with the three-dimensional flow of nanofluid over a bi-directional exponentially stretching sheet. The effects of Brownian motion and thermophoretic diffusion of nanoparticles are considered in the mathematical model. The temperature and nanoparticle volume fraction at the sheet are also distributed exponentially. Local similarity solutions are obtained by an implicit finite difference scheme known as Keller-box method. The results are compared with the existing studies in some limiting cases and found in good agreement. The results reveal the existence of interesting Sparrow-Gregg-type hills for temperature distribution corresponding to some range of parametric values. PMID:25785857
Ongoing hydrothermal heat loss from the 1912 ash-flow sheet, Valley of Ten Thousand Smokes, Alaska
Hogeweg, N.; Keith, T.E.C.; Colvard, E.M.; Ingebritsen, S.E.
2005-01-01
The June 1912 eruption of Novarupta filled nearby glacial valleys on the Alaska Peninsula with ash-flow tuff (ignimbrite), and post-eruption observations of thousands of steaming fumaroles led to the name 'Valley of Ten Thousand Smokes' (VTTS). By the late 1980s most fumarolic activity had ceased, but the discovery of thermal springs in mid-valley in 1987 suggested continued cooling of the ash-flow sheet. Data collected at the mid-valley springs between 1987 and 2001 show a statistically significant correlation between maximum observed chloride (Cl) concentration and temperature. These data also show a statistically significant decline in the maximum Cl concentration. The observed variation in stream chemistry across the sheet strongly implies that most solutes, including Cl, originate within the area of the VTTS occupied by the 1912 deposits. Numerous measurements of Cl flux in the Ukak River just below the ash-flow sheet suggest an ongoing heat loss of ???250 MW. This represents one of the largest hydrothermal heat discharges in North America. Other hydrothermal discharges of comparable magnitude are related to heat obtained from silicic magma bodies at depth, and are quasi-steady on a multidecadal time scale. However, the VTTS hydrothermal flux is not obviously related to a magma body and is clearly declining. Available data provide reasonable boundary and initial conditions for simple transient modeling. Both an analytical, conduction-only model and a numerical model predict large rates of heat loss from the sheet 90 years after deposition.
NASA Technical Reports Server (NTRS)
Reinath, M. S.; Ross, J. C.
1990-01-01
A flow visualization technique for the large wind tunnels of the National Full Scale Aerodynamics Complex (NFAC) is described. The technique uses a laser sheet generated by the NFAC Long Range Laser Velocimeter (LRLV) to illuminate a smoke-like tracer in the flow. The LRLV optical system is modified slightly, and a scanned mirror is added to generate the sheet. These modifications are described, in addition to the results of an initial performance test conducted in the 80- by 120-Foot Wind Tunnel. During this test, flow visualization was performed in the wake region behind a truck as part of a vehicle drag reduction study. The problems encountered during the test are discussed, in addition to the recommended improvements needed to enhance the performance of the technique for future applications.
Fe/V Redox Flow Battery Electrolyte Investigation and Optimization
Li, Bin; Li, Liyu; Wang, Wei; Nie, Zimin; Chen, Baowei; Wei, Xiaoliang; Luo, Qingtao; Yang, Zhenguo; Sprenkle, Vincent L.
2013-05-01
Recently invented Fe/V redox flow battery (IVBs) system has attracted more and more attentions due to its long-term cycling stability. In this paper, the factors (such as compositions, state of charge (SOC) and temperatures) influencing the stability of electrolytes in both positive and negative half-cells were investigated by an extensive matrix study. Thus an optimized electrolyte, which can be operated in the temperature ranges from -5oC to 50oC without any precipitations, was identified. The Fe/V flow cells using the optimized electrolytes and low-cost membranes exhibited satisfactory cycling performances at different temperatures. The efficiencies, capacities and energy densities of flow batteries with varying temperatures were discussed in detail.
OPTIMIZATION OF COAL PARTICLE FLOW PATTERNS IN LOW NOX BURNERS
Jost O.L. Wendt; Gregory E. Ogden; Jennifer Sinclair; Caner Yurteri
2001-08-20
The proposed research is directed at evaluating the effect of flame aerodynamics on NO{sub x} emissions from coal fired burners in a systematic manner. This fundamental research includes both experimental and modeling efforts being performed at the University of Arizona in collaboration with Purdue University. The objective of this effort is to develop rational design tools for optimizing low NO{sub x} burners to the kinetic emissions limit (below 0.2 lb./MMBTU). Experimental studies include both cold and hot flow evaluations of the following parameters: flame holder geometry, secondary air swirl, primary and secondary inlet air velocity, coal concentration in the primary air and coal particle size distribution. Hot flow experiments will also evaluate the effect of wall temperature on burner performance. Cold flow studies will be conducted with surrogate particles as well as pulverized coal. The cold flow furnace will be similar in size and geometry to the hot-flow furnace but will be designed to use a laser Doppler velocimeter/phase Doppler particle size analyzer. The results of these studies will be used to predict particle trajectories in the hot-flow furnace as well as to estimate the effect of flame holder geometry on furnace flow field. The hot-flow experiments will be conducted in a novel near-flame down-flow pulverized coal furnace. The furnace will be equipped with externally heated walls. Both reactors will be sized to minimize wall effects on particle flow fields. The cold-flow results will be compared with Fluent computation fluid dynamics model predictions and correlated with the hot-flow results with the overall goal of providing insight for novel low NO{sub x} burner geometry's.
NASA Astrophysics Data System (ADS)
Ali, Nasir; Khan, Sami Ullah; Abbas, Zaheer
2015-12-01
The aim of this article is to investigate the unsteady boundary layer flow and heat transfer analysis in a third grade fluid over an oscillatory stretching sheet under the influences of thermal radiation and heat source/sink. The convective boundary condition at the sheet is imposed to determine the temperature distribution. Homotopy analysis method (HAM) is used to solve dimensionless nonlinear partial differential equations. The effects of involved parameters on both velocity and temperature fields are illustrated in detail through various plots. It is found that the amplitude of velocity decreases by increasing the ratio of the oscillation frequency of the sheet to its stretching rate and Hartmann number while it increases by increasing the third grade fluid parameter. On contrary, the temperature field is found to be a decreasing function of the third grade fluid parameter.
NASA Astrophysics Data System (ADS)
Hu, Chenghang
2003-04-01
The light sheet technique provides a unique method of visualization for off-body flow fields at subsonic through supersonic speeds. But conventional mirror tansmission laser systems have some shortcomings: The harsh environments of high speed wind tunnels often cause the misalignment of the optical components and the contamination of the mirror surfaces. The exposed laser beam is dangerous to the persons at the work sites. This paper presents an advanced optical-fiber-transmission laser sheet system, which provides a solution to the problems above and greatly improves the quality, safety and reliability of the light sheet. The emphasis is laid on the detailed composition of the new type visualization system. Some examples of its applications in transonic/supersonic wind tunnels are also given in this paper.
Isa, Sharena Mohamad; Ali, Anati
2015-10-22
In this paper, the hydromagnetic flow of dusty fluid over a vertical stretching sheet with thermal radiation is investigated. The governing partial differential equations are reduced to nonlinear ordinary differential equations using similarity transformation. These nonlinear ordinary differential equations are solved numerically using Runge-Kutta Fehlberg fourth-fifth order method (RKF45 Method). The behavior of velocity and temperature profiles of hydromagnetic fluid flow of dusty fluid is analyzed and discussed for different parameters of interest such as unsteady parameter, fluid-particle interaction parameter, the magnetic parameter, radiation parameter and Prandtl number on the flow.
NASA Astrophysics Data System (ADS)
Grant, I.; Parkin, P.; Wang, X.
Experimental studies have been conducted on a 0.9 m diameter, horizontal axis wind turbine (HAWT) placed in the open jet of a closed return wind tunnel. The turbine was tested in a three blade and a two blade configuration. The power coefficient of the turbine was measured and wake flow studies conducted for a range of yawed flows by tilting the rotor plane at various angles up to 30° to the incident wind direction. The motion of the shed vorticity was followed using laser-sheet flow visualisation with the overall wake deflection being measured. The results were compared with theoretical predictions and with studies conducted elsewhere.
Security-constrained optimization. Added dimension in utility systems optimal power flow
Degeneff, R.C.; Neugebauer, W. ); Saylor, C.H.; Corey, S.L.
1988-10-01
Compared to the tempered environment of the late 1960s and early 1970s, the 1980s have been, and will continue to be, a time of challenge for utilities. Today's utility executive most confront a spectrum of technical issues, ranging from wheeling and transmission line access to loop flow. There are other challenges to face. The traditional utility corporate structure is being reorganized, with utility staffs shrinking in size. And public scrutiny has become more intense as public bodies question the technical and environmental impact, as well as the financial and legal prudence of a utility's activities. Utilities are successfully meeting these challenges and becoming more productive, due, in part to their use of innovative computer programs and tools. One of these tools is an optimal power flow (OPF). The following describes a new dimension in the optimal power flow technology known as the security-constrained optimization (SCO) program.
Wing-section optimization for supersonic viscous flows
NASA Technical Reports Server (NTRS)
Item, Cem C.
1995-01-01
The recent interest in High Speed Civil Transport (HSCT) has resulted in renewed research studies of optimized supersonic cruise transport configurations. Incorporation of flow viscosity effects in the design process of such a supersonic wing is currently under investigation. This may lead to more accurate problem formulations and, in turn, greater aerodynamic efficiency than can be obtained by the traditional, inviscid, linear theories. In this context, for a design code to be a candidate for a complex optimization problem, such as three-dimensional viscous supersonic wing design, it should be validated using simpler building-block shapes. To optimize the shape of a supersonic wing, an automated method that also includes higher fidelity to the flow physics is desirable. With this impetus, an aerodynamic optimization methodology incorporating Navier-Stokes equations and sensitivity analysis had been previously developed. Prior to embarking upon the wing design task, the present investigation concentrated on testing the flexibility of the methodology, and the identification of adequate problem formulations, by defining two-dimensional, cost-effective test cases. Starting with two distinctly different initial airfoils, two independent shape optimizations resulted in shapes with very similar features. Secondly, the normal section to the subsonic portion of the leading edge, which had a high normal angle-of-attack, was considered. The optimization resulted in a shape with twist and camber, which eliminated the adverse pressure gradient, hence, exploiting the leading-edge thrust. The wing section shapes obtained in all the test cases had the features predicted by previous studies. Therefore, it was concluded that the flowfield analyses and the sensitivity coefficients were computed and fed to the present gradient-based optimizer correctly. Also, as a result of the present two-dimensional study, suggestions were made for problem formulations which should contribute to an
Optimized open-flow mixing: insights from microbubble streaming
NASA Astrophysics Data System (ADS)
Rallabandi, Bhargav; Wang, Cheng; Guo, Lin; Hilgenfeldt, Sascha
2015-11-01
Microbubble streaming has been developed into a robust and powerful flow actuation technique in microfluidics. Here, we study it as a paradigmatic system for microfluidic mixing under a continuous throughput of fluid (open-flow mixing), providing a systematic optimization of the device parameters in this practically important situation. Focusing on two-dimensional advective stirring (neglecting diffusion), we show through numerical simulation and analytical theory that mixing in steady streaming vortices becomes ineffective beyond a characteristic time scale, necessitating the introduction of unsteadiness. By duty cycling the streaming, such unsteadiness is introduced in a controlled fashion, leading to exponential refinement of the advection structures. The rate of refinement is then optimized for particular parameters of the time modulation, i.e. a particular combination of times for which the streaming is turned ``on'' and ``off''. The optimized protocol can be understood theoretically using the properties of the streaming vortices and the throughput Poiseuille flow. We can thus infer simple design principles for practical open flow micromixing applications, consistent with experiments. Current Address: Mechanical and Aerospace Engineering, Princeton University.
Optimization of the Mini-Flo flow cytometer
Venkatesh, M.
1996-06-01
A new method of collecting light scattering from a liquid flow cytometer has been proposed; this apparatus is named the Mini-Flo flow cytometer. The Mini-Flo uses a high numerical aperture collection immersed in the flow stream. The collector consists of a conically tipped fiber optic pipe and terminating optical detector. This study was performed to improve the signal/noise ration and optimize the Mini-Flo`s performance for HIV blood detection applications. Experiments were performed to gauge the effects of Raman scattering, lens/filter fluorescence, and fiber optic fluorescence on the Mini-Flo`s performance and signal/noise ratio. Results indicated that the fiber optic was a major source of fluorescence noise and reducing its length from 33 cm to 10 cm increased the signal noise ratio from 8 to 75. Therefore, one of the key issues in optimizing the Mini-Flo`s performance is a redesign of the holding structure such that the fiber optic length is minimized. Further improvements of the Mini-Flo`s performance can be achieved by studying the polish of the fiber optic, the flow over the fiber optics`s conical tip, and the optimal particle rates.
Epidotisation and fluid flow in sheeted dyke complex : new field and experimental constraints
NASA Astrophysics Data System (ADS)
Coelho, Gabriel; Sizaret, Stanislas; Arbaret, Laurent; Branquet, Yannick; Champallier, Rémi
2013-04-01
Hydrothermal system in oceanic crust is usually studied via dredge samples and drilled holes but their equivalent are also found in ophiolitic complexes (Oman, Cyprus). In the deepest zone, the fluids react with the sheeted diabase dikes at 400°C and 400 bars to form epidosites by enrichment in epidote and quartz [1]. Mineralogy and chemistry of epidosites have been widely studied on fields [1] and hydrology is generally studied using numerical models [2]. However, the relations and the timing of the emplacement of diabase dikes, their alteration in epidosite and the regional deformation remain unclear. We performed experiments on diabase sampled in the Troodos complex (Cyprus), 1) to stress the P-T-fO2-fluid composition conditions of the reaction of epidotisation and, 2) to quantify interrelations between the permeability and the epidotisation during deformation. In Troodos, we observed two major types of epidosite: 1) a pervasive epidosite in the core of dikes and a banding which is parallel to chilled margins and, 2) assemblages of epidote and quartz as alteration fronts in cooling joints or in the form of veins cross-cutting non-epidotised dikes. This last type of epidotisation clearly appears to be a hydrothermal veining process. We synthesized epidote in a static autoclave with external heating at 500°C and 2500 bars. Epidote was formed by the following reaction: 6 albite + 2 hematite + anorthite + 7 Ca2+ + 6 H2O → 4 epidote + 8 quartz + 6 Na+ + 8 H+. The calculated variation of the molar volume is about -3% (creation of porosity). Two parameters are essential to synthesize epidote from diabase: the oxygen fugacity and the composition of the fluid (enriched in Ca and Fe). However, there is an obvious problem of nucleation at 400°C and 400 bars. In order to understand how fluid flows throughout sheeted dikes, in situ measurements of permeability during coaxial deformation have been performed in a Paterson apparatus by infiltration of Argon and water. The
Design optimization of axisymmetric bodies in nonuniform transonic flow
NASA Technical Reports Server (NTRS)
Lan, C. Edward
1989-01-01
An inviscid transonic code capable of designing an axisymmetric body in a uniform or nonuniform flow was developed. The design was achieved by direct optimiation by coupling an analysis code with an optimizer. Design examples were provided for axisymmetric bodies with fineness ratios of 8.33 and 5 at different Mach numbers. It was shown that by reducing the nose radius and increasing the afterbody thickness of initial shapes obtained from symmetric NACA four-digit airfoil contours, wave drag could be reduced by 29 percent for a body of fineness ratio 8.33 in a nonuniform transonic flow of M = 0.98 to 0.995. The reduction was 41 percent for a body of fineness ratio 5 in a uniform transonic flow of M = 0.925 and 65 percent for the same body but in a nonuniform transonic flow of M = 0.90 to 0.95.
Systematic study of source mask optimization and verification flows
NASA Astrophysics Data System (ADS)
Ben, Yu; Latypov, Azat; Chua, Gek Soon; Zou, Yi
2012-06-01
Source mask optimization (SMO) emerged as powerful resolution enhancement technique (RET) for advanced technology nodes. However, there is a plethora of flow and verification metrics in the field, confounding the end user of the technique. Systemic study of different flows and the possible unification thereof is missing. This contribution is intended to reveal the pros and cons of different SMO approaches and verification metrics, understand the commonality and difference, and provide a generic guideline for RET selection via SMO. The paper discusses 3 different type of variations commonly arise in SMO, namely pattern preparation & selection, availability of relevant OPC recipe for freeform source and finally the metrics used in source verification. Several pattern selection algorithms are compared and advantages of systematic pattern selection algorithms are discussed. In the absence of a full resist model for SMO, alternative SMO flow without full resist model is reviewed. Preferred verification flow with quality metrics of DOF and MEEF is examined.
MHD heat and mass transfer flow over a permeable stretching/shrinking sheet with radiation effect
NASA Astrophysics Data System (ADS)
Mat Yasin, Mohd Hafizi; Ishak, Anuar; Pop, Ioan
2016-06-01
The steady two-dimensional magnetohydrodynamic (MHD) flow past a permeable stretching/shrinking sheet with radiation effects is investigated. The similarity transformation is introduced to transform the governing partial differential equations into a system of ordinary differential equations before being solved numerically using a shooting method. The results are obtained for the skin friction coefficient, the local Nusselt number and the local Sherwood number as well as the velocity, temperature and the concentration profiles for some values of the governing parameters, namely, suction/injection parameter S, stretching/shrinking parameter λ, magnetic parameter M, radiation parameter R, heat source/sink Q and chemical rate parameter K. For the shrinking case, there exist two solutions for a certain range of parameters, but the solution is unique for the stretching case. The stability analysis verified that the upper branch solution is linearly stable and physically reliable while the lower branch solution is not. For the reliable solution, the skin friction coefficient increases in the present of magnetic field. The heat transfer rate at the surface decreases in the present of radiation.
Flow and Heat Transfer to Sisko Nanofluid over a Nonlinear Stretching Sheet.
Khan, Masood; Malik, Rabia; Munir, Asif; Khan, Waqar Azeem
2015-01-01
The two-dimensional boundary layer flow and heat transfer to Sisko nanofluid over a non-linearly stretching sheet is scrutinized in the concerned study. Our nanofluid model incorporates the influences of the thermophoresis and Brownian motion. The convective boundary conditions are taken into account. Implementation of suitable transformations agreeing with the boundary conditions result in reduction of the governing equations of motion, energy and concentration into non-linear ordinary differential equations. These coupled non-linear ordinary differential equations are solved analytically by using the homotopy analysis method (HAM) and numerically by the shooting technique. The effects of the thermophoresis and Brownian motion parameters on the temperature and concentration fields are analyzed and graphically presented. The secured results make it clear that the temperature distribution is an increasing function of the thermophoresis and Brownian motion parameters and concentration distribution increases with the thermophoresis parameter but decreases with the Brownian motion parameter. To see the validity of the present work, we made a comparison with the numerical results as well as previously published work with an outstanding compatibility. PMID:25993658
Flow and Heat Transfer to Sisko Nanofluid over a Nonlinear Stretching Sheet
Khan, Masood; Malik, Rabia; Munir, Asif; Khan, Waqar Azeem
2015-01-01
The two-dimensional boundary layer flow and heat transfer to Sisko nanofluid over a non-linearly stretching sheet is scrutinized in the concerned study. Our nanofluid model incorporates the influences of the thermophoresis and Brownian motion. The convective boundary conditions are taken into account. Implementation of suitable transformations agreeing with the boundary conditions result in reduction of the governing equations of motion, energy and concentration into non-linear ordinary differential equations. These coupled non-linear ordinary differential equations are solved analytically by using the homotopy analysis method (HAM) and numerically by the shooting technique. The effects of the thermophoresis and Brownian motion parameters on the temperature and concentration fields are analyzed and graphically presented. The secured results make it clear that the temperature distribution is an increasing function of the thermophoresis and Brownian motion parameters and concentration distribution increases with the thermophoresis parameter but decreases with the Brownian motion parameter. To see the validity of the present work, we made a comparison with the numerical results as well as previously published work with an outstanding compatibility. PMID:25993658
NASA Astrophysics Data System (ADS)
Hughes, T.; Sargent, A.; Fastook, J.; Purdon, K.; Li, J.; Yan, J.-B.; Gogineni, S.
2015-08-01
The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier-Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.
NASA Astrophysics Data System (ADS)
Hughes, T.; Sargent, A.; Fastook, J.; Purdon, K.; Li, J.; Yan, J.-B.; Gogineni, S.
2016-01-01
The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling along flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier-Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.
Rosenbaum, J.G.
1993-07-10
Rock magnetic studies of tuffs are essential to the interpretation of paleomagnetic data derived from such rocks, provide a basis for interpretation of aeromagnetic data over volcanic terranes, and yield insights into the depositional and cooling histories of ash flow sheets. A rhyolitic ash flow sheet, the Miocene-aged Tiva Canyon Member of the Paintbrush Tuff, contains both titanomagnetite phenocrysts, present in the magma prior to eruption, and cubic Fe-oxide microcrystals that grew after emplacement. Systematic variations in the quantity and magnetic grain size of the microcrystals produce large variations in magnetic properties through a section of the ash flow sheet penetrated in a borehole on the Nevada Test Site. Natural remanent magnetization varies from less than 1 x 10{sup {minus}4} to more than 8 x 10{sup {minus}4} A m{sup 3} kg{sup {minus}1}, and in-phase magnetic susceptibility varies from less than 1 x 10{sup {minus}6} to more than 10 x 10{sup {minus}6} m{sup 3} kg{sup {minus}1}. The microcrystals, which include both magnetite and maghemite, have Curie points and maximum unblocking temperatures between 580{degrees}C and 640{degrees}C. Rock magnetic data, including in-phase and quadrature magnetic susceptibilities as well as hysteresis parameters, demonstrate that these microcrystals are of superparamagnetic and single-domain sizes. Titanomagnetite phenocrysts are the dominant remanence carriers in the central 50 m of the section, whereas microcrystals are important contributors to remanent magnetization and magnetic susceptibility in two 15-m-thick zones at the top and bottom. Within these zones the size of microcrystals decreases both toward the quenched margins and toward the interior of the sheet. The decrease in microcrystal size toward the interior of the sheet is interpreted to indicate the presence of a cooling break; possibly represented by a concentration of pumice. 32 refs., 11 figs.
Optimization of micropillar sequences for fluid flow sculpting
NASA Astrophysics Data System (ADS)
Stoecklein, Daniel; Wu, Chueh-Yu; Kim, Donghyuk; Di Carlo, Dino; Ganapathysubramanian, Baskar
2016-01-01
Inertial fluid flow deformation around pillars in a microchannel is a new method for controlling fluid flow. Sequences of pillars have been shown to produce a rich phase space with a wide variety of flow transformations. Previous work has successfully demonstrated manual design of pillar sequences to achieve desired transformations of the flow cross section, with experimental validation. However, such a method is not ideal for seeking out complex sculpted shapes as the search space quickly becomes too large for efficient manual discovery. We explore fast, automated optimization methods to solve this problem. We formulate the inertial flow physics in microchannels with different micropillar configurations as a set of state transition matrix operations. These state transition matrices are constructed from experimentally validated streamtraces for a fixed channel length per pillar. This facilitates modeling the effect of a sequence of micropillars as nested matrix-matrix products, which have very efficient numerical implementations. With this new forward model, arbitrary micropillar sequences can be rapidly simulated with various inlet configurations, allowing optimization routines quick access to a large search space. We integrate this framework with the genetic algorithm and showcase its applicability by designing micropillar sequences for various useful transformations. We computationally discover micropillar sequences for complex transformations that are substantially shorter than manually designed sequences. We also determine sequences for novel transformations that were difficult to manually design. Finally, we experimentally validate these computational designs by fabricating devices and comparing predictions with the results from confocal microscopy.
NASA Astrophysics Data System (ADS)
Abd Elazem, Nader Y.
2016-06-01
The flow of nanofluids past a stretching sheet has attracted much attention owing to its wide applications in industry and engineering. Numerical solution has been discussed in this article for studying the effect of suction (or injection) on flow of nanofluids past a stretching sheet. The numerical results carried out using Chebyshev collocation method (ChCM). Useful results for temperature profile, concentration profile, reduced Nusselt number, and reduced Sherwood number are discussed in tabular and graphical forms. It was also demonstrated that both temperature and concentration profiles decrease by an increase from injection to suction. Moreover, the numerical results show that the temperature profiles decrease at high values of Prandtl number Pr. Finally, the present results showed that the reduced Nusselt number is a decreasing function, whereas the reduced Sherwood number is an increasing function at fixed values of Prandtl number Pr, Lewis number Le and suction (or injection) parameter s for variation of Brownian motion parameter Nb, and thermophoresis parameter Nt.
NASA Astrophysics Data System (ADS)
Mabood, F.; Khan, W. A.; Ismail, A. I. M.
2015-01-01
The MHD laminar boundary layer flow with heat and mass transfer of an electrically conducting water-based nanofluid over a nonlinear stretching sheet with viscous dissipation effect is investigated numerically. This is the extension of the previous study on flow and heat transfer of a nanofluid over nonlinear stretching sheet (Rana and Bhargava, Commun. Nonlinear Sci. Numer. Simul. 17 (2012) 212-226). The governing equations are reduced to nonlinear ordinary differential equations using suitable similarity transformation. The effects of the governing parameters on dimensionless quantities like velocity, temperature, nanoparticle concentration, friction factor, local Nusselt, and Sherwood numbers are explored. It is found that the dimensionless velocity decreases and temperature increases with magnetic parameter, and the thermal boundary layer thickness increases with Brownian motion and thermophoresis parameters.
Artificial Bee Colony Algorithm for Solving Optimal Power Flow Problem
Le Dinh, Luong; Vo Ngoc, Dieu
2013-01-01
This paper proposes an artificial bee colony (ABC) algorithm for solving optimal power flow (OPF) problem. The objective of the OPF problem is to minimize total cost of thermal units while satisfying the unit and system constraints such as generator capacity limits, power balance, line flow limits, bus voltages limits, and transformer tap settings limits. The ABC algorithm is an optimization method inspired from the foraging behavior of honey bees. The proposed algorithm has been tested on the IEEE 30-bus, 57-bus, and 118-bus systems. The numerical results have indicated that the proposed algorithm can find high quality solution for the problem in a fast manner via the result comparisons with other methods in the literature. Therefore, the proposed ABC algorithm can be a favorable method for solving the OPF problem. PMID:24470790
Artificial bee colony algorithm for solving optimal power flow problem.
Le Dinh, Luong; Vo Ngoc, Dieu; Vasant, Pandian
2013-01-01
This paper proposes an artificial bee colony (ABC) algorithm for solving optimal power flow (OPF) problem. The objective of the OPF problem is to minimize total cost of thermal units while satisfying the unit and system constraints such as generator capacity limits, power balance, line flow limits, bus voltages limits, and transformer tap settings limits. The ABC algorithm is an optimization method inspired from the foraging behavior of honey bees. The proposed algorithm has been tested on the IEEE 30-bus, 57-bus, and 118-bus systems. The numerical results have indicated that the proposed algorithm can find high quality solution for the problem in a fast manner via the result comparisons with other methods in the literature. Therefore, the proposed ABC algorithm can be a favorable method for solving the OPF problem. PMID:24470790
Optimizing the flow in a liquid sodium dynamo experiment
NASA Astrophysics Data System (ADS)
Taylor, N. Zane
The Madison Dynamo experiment drives a turbulent flow of liquid sodium in a sphere in order to observe a MHD dynamo instability: An exponentially growing magnetic field at the expense of kinetic energy. Initial runs of the experiment observed intermittent bursts of the predicted magnetic mode, but no self-excited field was observed. It was found that turbulent fluctuations were producing large-scale magnetic fields that were a significant fraction of the magnitude of the fields induced by the mean flow. These turbulent-induced fields were solely detrimental, opposing the generation of the magnetic field produced by the mean flow. Baffles and vanes were added to the experiment to optimize the helical pitch of the mean flow and to remove the large-scale detrimental fluctuations. The observed drop in required motor power and a drop in specific measured magnetic response modes gives direct confirmation that these large detrimental eddies have been removed. A probe was developed to characterize the turbulence in the MDE after the baffles were installed and it was determined that the remaining turbulent EMF was mostly acting as an enhanced dissipation to the induced magnetic field. After these modifications, the induced magnetic field produced by the flowing sodium interacting with a seed magnetic field now closely matches laminar predictions. However, no self-excited field has been observed. A velocity inversion technique has been developed that compares internal and external field measurements with a predictive model and determines what the effective mean flow is in the experiment. Results from this velocity inversion give another metric on how optimized the flow profile is and also provide the most robust method of determining how close the experiment is to achieving a dynamo.
Resistive Network Optimal Power Flow: Uniqueness and Algorithms
Tan, CW; Cai, DWH; Lou, X
2015-01-01
The optimal power flow (OPF) problem minimizes the power loss in an electrical network by optimizing the voltage and power delivered at the network buses, and is a nonconvex problem that is generally hard to solve. By leveraging a recent development on the zero duality gap of OPF, we propose a second-order cone programming convex relaxation of the resistive network OPF, and study the uniqueness of the optimal solution using differential topology, especially the Poincare-Hopf Index Theorem. We characterize the global uniqueness for different network topologies, e.g., line, radial, and mesh networks. This serves as a starting point to design distributed local algorithms with global behaviors that have low complexity, are computationally fast, and can run under synchronous and asynchronous settings in practical power grids.
Analysis of the Hessian for Aerodynamic Optimization: Inviscid Flow
NASA Technical Reports Server (NTRS)
Arian, Eyal; Ta'asan, Shlomo
1996-01-01
In this paper we analyze inviscid aerodynamic shape optimization problems governed by the full potential and the Euler equations in two and three dimensions. The analysis indicates that minimization of pressure dependent cost functions results in Hessians whose eigenvalue distributions are identical for the full potential and the Euler equations. However the optimization problems in two and three dimensions are inherently different. While the two dimensional optimization problems are well-posed the three dimensional ones are ill-posed. Oscillations in the shape up to the smallest scale allowed by the design space can develop in the direction perpendicular to the flow, implying that a regularization is required. A natural choice of such a regularization is derived. The analysis also gives an estimate of the Hessian's condition number which implies that the problems at hand are ill-conditioned. Infinite dimensional approximations for the Hessians are constructed and preconditioners for gradient based methods are derived from these approximate Hessians.
NASA Astrophysics Data System (ADS)
Taherizadeh, Aboozar; Green, Daniel E.; Yoon, Jeong W.
2013-12-01
A material model for more effective analysis of plastic deformation of sheet materials is presented in this paper. The model is capable of considering the following aspects of plastic deformation behavior of sheet materials: the anisotropy in yielding stresses in different directions by using a quadratic yield function (based on Hill's 1948 model and stress ratios), the anisotropy in work hardening by introducing non-constant flow stress hardening in different directions, the anisotropy in plastic strains in different directions by using a quadratic plastic potential function and non-associated flow rule (based on Hill's 1948 model and plastic strain ratios, r-values), and finally some of the cyclic hardening phenomena such as Bauschinger's effect and transient behavior for reverse loading by using a coupled nonlinear kinematic hardening (so-called Armstrong-Frederick-Chaboche model). Basic fundamentals of the plasticity of the model are presented in a general framework. Then, the model adjustment procedure is derived for the plasticity formulations. Also, a generic numerical stress integration procedure is developed based on backward-Euler method (so-called multi-stage return mapping algorithm). Different aspects of the model are verified for DP600 steel sheet. Results show that the new model is able to predict the sheet material behavior in both anisotropic hardening and cyclic hardening regimes more accurately. By featuring the above-mentioned facts in the presented constitutive model, it is expected that more accurate results can be obtained by implementing this model in computational simulations of sheet material forming processes. For instance, more precise results of springback prediction of the parts formed from highly anisotropic hardened materials or that of determining the forming limit diagrams is highly expected by using the developed material model.
NASA Astrophysics Data System (ADS)
Pick, Simon; Lehmann, Fritz-Olaf
2009-12-01
Non-scanning volume flow measurement techniques such as 3D-PTV, holographic and tomographic particle image velocimetry (PIV) permit reconstructions of all three components (3C) of velocity and vorticity vectors in a fluid volume (3D). In this study, we present a novel 3D3C technique termed Multiple-Color-Plane Stereo Particle-Image-Velocimetry (color PIV), which allows instantaneous measurements of 3C velocity vectors in six parallel, colored light sheets. We generated the light sheets by passing white light of two strobes through dichroic color filters and imaged the slices by two 3CCD color cameras in Stereo-PIV configuration. The stereo-color images were processed by custom software routines that sorted each colored fluid particle into one of six gray-scale images according to its hue, saturation, and luminance. We used conventional Stereo PIV cross-correlation algorithms to compute a 3D planar vector field for each light sheet and subsequently interpolated a volume flow map from the six vector fields. As a first application, we quantified the wake and axial flow in the vortical structures of a robotic insect (fruit fly) model wing. In contrast to previous findings, the measured data indicate strong axial flow components on the upper wing surface, including axial flow in the leading-edge vortex core. Collectively, color PIV is robust against mechanical misalignments, avoids laser safety issues, and computes instantaneous 3D vector fields in a fraction of the time typical for other 3D systems. Color PIV might thus be of value for volume measurements of highly unsteady flows.
Adjoint-based airfoil shape optimization in transonic flow
NASA Astrophysics Data System (ADS)
Gramanzini, Joe-Ray
The primary focus of this work is efficient aerodynamic shape optimization in transonic flow. Adjoint-based optimization techniques are employed on airfoil sections and evaluated in terms of computational accuracy as well as efficiency. This study examines two test cases proposed by the AIAA Aerodynamic Design Optimization Discussion Group. The first is a two-dimensional, transonic, inviscid, non-lifting optimization of a Modified-NACA 0012 airfoil. The second is a two-dimensional, transonic, viscous optimization problem using a RAE 2822 airfoil. The FUN3D CFD code of NASA Langley Research Center is used as the ow solver for the gradient-based optimization cases. Two shape parameterization techniques are employed to study their effect and the number of design variables on the final optimized shape: Multidisciplinary Aerodynamic-Structural Shape Optimization Using Deformation (MASSOUD) and the BandAids free-form deformation technique. For the two airfoil cases, angle of attack is treated as a global design variable. The thickness and camber distributions are the local design variables for MASSOUD, and selected airfoil surface grid points are the local design variables for BandAids. Using the MASSOUD technique, a drag reduction of 72.14% is achieved for the NACA 0012 case, reducing the total number of drag counts from 473.91 to 130.59. Employing the BandAids technique yields a 78.67% drag reduction, from 473.91 to 99.98. The RAE 2822 case exhibited a drag reduction from 217.79 to 132.79 counts, a 39.05% decrease using BandAids.
Self-Contained Automated Methodology for Optimal Flow Control
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.; Gunzburger, Max D.; Nicolaides, Roy A.; Erlebacherl, Gordon; Hussaini, M. Yousuff
1997-01-01
This paper describes a self-contained, automated methodology for active flow control which couples the time-dependent Navier-Stokes system with an adjoint Navier-Stokes system and optimality conditions from which optimal states, i.e., unsteady flow fields and controls (e.g., actuators), may be determined. The problem of boundary layer instability suppression through wave cancellation is used as the initial validation case to test the methodology. Here, the objective of control is to match the stress vector along a portion of the boundary to a given vector; instability suppression is achieved by choosing the given vector to be that of a steady base flow. Control is effected through the injection or suction of fluid through a single orifice on the boundary. The results demonstrate that instability suppression can be achieved without any a priori knowledge of the disturbance, which is significant because other control techniques have required some knowledge of the flow unsteadiness such as frequencies, instability type, etc. The present methodology has been extended to three dimensions and may potentially be applied to separation control, re-laminarization, and turbulence control applications using one to many sensors and actuators.
Nadeem, Sohail; Ul Haq, Rizwan; Akbar, Noreen Sher; Lee, Changhoon; Khan, Zafar Hayat
2013-01-01
In the present article, we considered two-dimensional steady incompressible Oldroyd-B nanofluid flow past a stretching sheet. Using appropriate similarity variables, the partial differential equations are transformed to ordinary (similarity) equations, which are then solved numerically. The effects of various parameters, namely, Deborah numbers and , Prandtl parameter , Brownian motion , thermophoresis parameter and Lewis number , on flow and heat transfer are investigated. To see the validity of the present results, we have made the comparison of present results with the existing literature. PMID:24015172
NASA Astrophysics Data System (ADS)
Zaimi, Khairy; Bakar, Nor Ashikin Abu
2015-05-01
This paper deals with the magnetohydrodynamic (MHD) stagnation point flow and heat transfer towards a permeable stretching sheet in a nanofluid. By using a similarity transformation, the governing equations of fluid flow are reduced into ordinary differential equation, which are then solved numerically using a shooting method. The effects of suction/injection parameter on the velocity, temperature and concentration profiles and heat transfer characteristics are obtained and graphically presented. It is found that skin friction coefficient and the local Nusselt number increase with suction, while it acts in opposite manner with injection.
NASA Astrophysics Data System (ADS)
Aini Mat, Nor Azian; Arifin, Norihan Md.; Nazar, Roslinda; Ismail, Fudziah; Bachok, Norfifah
2013-09-01
A similarity solution of the steady magnetohydrodynamic (MHD) mixed convection boundary layer flow due to a stretching vertical heated sheet in a power law nanofluid with thermal radiation effect is theoretically studied. The governing system of partial differential equations is first transformed into a system of ordinary differential equations. The transformed equations are solved numerically using the shooting method. The influence of pertinent parameters such as the nanoparticle volume fraction parameter, the magnetic parameter, the buoyancy or mixed convection parameter and the radiation parameter on the flow and heat transfer characteristics is discussed. Comparisons with published results are also presented.
NASA Astrophysics Data System (ADS)
Hashim, Hasmawani; Mohamed, Muhammad Khairul Anuar; Hussanan, Abid; Ishak, Nazila; Sarif, Norhafizah Md; Salleh, Mohd Zuki
2015-12-01
The stagnation point flow of a vicous fluid towards a stretching sheet with slip conditions and viscous dissipation is studied. With the help of similarity transformation, the govering equations are converted to nonlinear ordinary differential equations and then solved numerically by Runge-Kutta-Fehlberg (RKF) technique. Numerical results for the local Nusselt number and skin friction coefficient as well as the temperature and velocity field are elucidated through tables and graphs. The influence of Prandtl number, stretching parameter, Eckert number, thermal and velocity slip parameter on the flow and heat transfer characteristics are analyzed and discussed.
NASA Astrophysics Data System (ADS)
Naramgari, Sandeep; Sulochana, C.
2016-01-01
In this study, we analyzed the heat and mass transfer in thermophoretic radiative hydromagnetic nanofluid flow over an exponentially stretching porous sheet embedded in porous medium with internal heat generation/absorption, viscous dissipation and suction/injection effects. The governing partial differential equations of the flow are converted into nonlinear coupled ordinary differential equations by using similarity transformation. Runge-Kutta-based shooting technique is employed to yield the numerical solutions for the model. The effect of non-dimensional parameters on velocity, temperature and concentration profiles are discussed and presented through graphs. The physical quantities of interest local skin friction coefficient, Nusselt and Sherwood numbers are calculated and presented through tables.
Multi-Objective Parallel Test-Sheet Composition Using Enhanced Particle Swarm Optimization
ERIC Educational Resources Information Center
Ho, Tsu-Feng; Yin, Peng-Yeng; Hwang, Gwo-Jen; Shyu, Shyong Jian; Yean, Ya-Nan
2009-01-01
For large-scale tests, such as certification tests or entrance examinations, the composed test sheets must meet multiple assessment criteria. Furthermore, to fairly compare the knowledge levels of the persons who receive tests at different times owing to the insufficiency of available examination halls or the occurrence of certain unexpected…
ERIC Educational Resources Information Center
Yin, Peng-Yeng; Chang, Kuang-Cheng; Hwang, Gwo-Jen; Hwang, Gwo-Haur; Chan, Ying
2006-01-01
To accurately analyze the problems of students in learning, the composed test sheets must meet multiple assessment criteria, such as the ratio of relevant concepts to be evaluated, the average discrimination degree, difficulty degree and estimated testing time. Furthermore, to precisely evaluate the improvement of student's learning performance…
NASA Astrophysics Data System (ADS)
Das, Deya; Hardikar, Rahul; Han, Sang Soo; Lee, Kwang Ryeol; Singh, Abhishek Kumar
Boron doped graphene shows better adsorption of Li compared to pristine graphene and has been investigated as a potential anode material for Li-ion batteries. Using first principles density functional theory calculations, we investigate the effect of increasing boron concentration on the gravimetric capacity of mono-layered boron doped graphene sheets, BCx (x = 7, 5, 3, 2 and 1). Li storage capacity increases with the increase in boron concentration giving highest capacity for monolayer BC2 (~ 1400 mAh/g), and is about 1.6 times higher than previously reported capacity of BC3. This is due to the more number of available empty states above the Fermi level in BC2 compared to other sheets. Moreover, owing to a very low Li diffusion barrier, the Li kinetics in BC2 is also found to be better among all the layered boron doped carbon sheets. Further enhancement of B concentration, as in BC, leads to strong binding of Li, thereby hindering the delithiation processes. Hence, BC2 with optimal concentration of B among the BCx phases, emerges as a promising choice for anode material in rechargeable Li ion battery.
Wing-section optimization for supersonic viscous flow
NASA Technical Reports Server (NTRS)
Item, Cem C.; Baysal, Oktay (Editor)
1995-01-01
To improve the shape of a supersonic wing, an automated method that also includes higher fidelity to the flow physics is desirable. With this impetus, an aerodynamic optimization methodology incorporating thin-layer Navier-Stokes equations and sensitivity analysis had been previously developed. Prior to embarking upon the wind design task, the present investigation concentrated on testing the feasibility of the methodology, and the identification of adequate problem formulations, by defining two-dimensional, cost-effective test cases. Starting with two distinctly different initial airfoils, two independent shape optimizations resulted in shapes with similar features: slightly cambered, parabolic profiles with sharp leading- and trailing-edges. Secondly, the normal section to the subsonic portion of the leading edge, which had a high normal angle-of-attack, was considered. The optimization resulted in a shape with twist and camber which eliminated the adverse pressure gradient, hence, exploiting the leading-edge thrust. The wing section shapes obtained in all the test cases had the features predicted by previous studies. Therefore, it was concluded that the flowfield analyses and sensitivity coefficients were computed and fed to the present gradient-based optimizer correctly. Also, as a result of the present two-dimensional study, suggestions were made for the problem formulations which should contribute to an effective wing shape optimization.
Opposed-Flow Flame Spread in a Narrow Channel Apparatus over Thin PMMA Sheets
NASA Technical Reports Server (NTRS)
Bornand, G. R.; Olson, Sandra L.; Miller, F. J.; Pepper, J. M.; Wichman, I. S.
2013-01-01
Flame spread tests have been conducted over polymethylmethacrylate (PMMA) samples in San Diego State University's Narrow Channel Apparatus (SDSU NCA). The Narrow Channel Apparatus (NCA) has the ability to suppress buoyant flow in horizontally spreading flames, and is currently being investigated as a possible replacement or complement to NASA's current material flammability test standard for non-metallic solids, NASA-STD-(I)-6001B Test 1. The buoyant suppression achieved with a NCA allows for tests to be conducted in a simulated microgravity atmosphere-a characteristic that Test 1 lacks since flames present in Test 1 are buoyantly driven. The SDSU NCA allows for flame spread tests to be conducted with varying opposed flow oxidizer velocities, oxygen percent by volume, and total pressure. Also, since the test sample is placed symmetrically between two confining plates so that there is a gap above and below the sample, this gap can be adjusted. This gap height adjustment allows for a compromise between heat loss from the flame to the confining boundaries and buoyancy suppression achieved by those boundaries. This article explores the effect gap height has on the flame spread rate for 75 µm thick PMMA at 1 atm pressure and 21% oxygen concentration by volume in the SDSU NCA. Flame spread results from the SDSU NCA for thin cellulose fuels have previously been compared to results from tests in actual microgravity at various test conditions with the same sample materials and were found to be in good agreement. This article also presents results from the SDSU NCA for PMMA at 1 atm pressure, opposed oxidizer velocity ranging from 3 to 35 cm/s, oxygen concentration by volume at 21%, 30 %, and 50% and fuel thicknesses of 50 and 75 µm. These results are compared to results obtained in actual microgravity for PMMA obtained at the 4.5s drop tower of MGLAB in Gifu, Japan, and the 5.2s drop tower at NASA's Zero-Gravity Research Facility in Cleveland, OH. This comparison confirms
NASA Technical Reports Server (NTRS)
Sergeev, V. A.; Lennartsson, W.; Pellinen, R.; Vallinkoski, M.; Fedorova, N. I.
1990-01-01
Average patterns of plasma drifts and auroral precipitation in the nightside auroral zone were constructed during a steady magnetospheric convection (SMC) event on February 19, 1978. By comparing these patterns with the measurements in the midtail plasma sheet made by ISEE-1, and using the corresponding magnetic field model, the following features are inferred: (1) the concentration of the earthward convection in the midnight portion of the plasma sheet (convection jet); (2) the depleted plasma energy content of the flux tubes in the convection jet region; and (3) the Region-1 field-aligned currents generated in the midtail plasma sheet. It is argued that these three elements are mutually consistent features appearing in the process of ionosphere-magnetosphere interaction during SMC periods. These configurational characteristics resemble the corresponding features of substorm expansions (enhanced convection and 'dipolarized' magnetic field within the substorm current wedge) and appear to play the same role in regulating the plasma flow in the flux tubes connected to the plasma sheet.
Model Assessment and Optimization Using a Flow Time Transformation
NASA Astrophysics Data System (ADS)
Smith, T. J.; Marshall, L. A.; McGlynn, B. L.
2012-12-01
Hydrologic modeling is a particularly complex problem that is commonly confronted with complications due to multiple dominant streamflow states, temporal switching of streamflow generation mechanisms, and dynamic responses to model inputs based on antecedent conditions. These complexities can inhibit the development of model structures and their fitting to observed data. As a result of these complexities and the heterogeneity that can exist within a catchment, optimization techniques are typically employed to obtain reasonable estimates of model parameters. However, when calibrating a model, the cost function itself plays a large role in determining the "optimal" model parameters. In this study, we introduce a transformation that allows for the estimation of model parameters in the "flow time" domain. The flow time transformation dynamically weights streamflows in the time domain, effectively stretching time during high streamflows and compressing time during low streamflows. Given the impact of cost functions on model optimization, such transformations focus on the hydrologic fluxes themselves rather than on equal time weighting common to traditional approaches. The utility of such a transform is of particular note to applications concerned with total hydrologic flux (water resources management, nutrient loading, etc.). The flow time approach can improve the predictive consistency of total fluxes in hydrologic models and provide insights into model performance by highlighting model strengths and deficiencies in an alternate modeling domain. Flow time transformations can also better remove positive skew from the streamflow time series, resulting in improved model fits, satisfaction of the normality assumption of model residuals, and enhanced uncertainty quantification. We illustrate the value of this transformation for two distinct sets of catchment conditions (snow-dominated and subtropical).
Optimal Control of Airfoil Flow Separation using Fluidic Excitation
NASA Astrophysics Data System (ADS)
Shahrabi, Arireza F.
as well as F+ were evaluated and discussed. The computational model predictions showed good agreement with the experimental data. It was observed that different angles of attack and flap angles have different requirements for the minimum value of the momentum coefficient, Cμ, in order for the SJA to be effective for control of separation. It was also found that the variation of F + noticeably affects the lift and drag forces acting on the airfoil. The optimum values of parameters during open loop control simulations have been applied in order to introduce the optimal open loop control outcome. An innovative approach has been implemented to formulate optimal frequencies and momentum ratios of vortex shedding which depends on angle of attack and static pressure of the separation zone in the upper chord. Optimal open loop results have been compared with the optimal closed loop results. Cumulative case studies in the matter of angle of attacks, flap angles, Re, Cμ and F+ provide a convincing collection of evidence to the following conclusion. An improvement of a direct closed loop control was demonstrated, and an analytical formula describing the properties of a separated flow and vortex shedding was proposed. Best AFC solutions are offered by providing optimal frequencies and momentum ratios at a variety of flow conditions.
Xiaolin Li; Speiser, T.W. NOAA/SEL, Boulder, CO )
1991-11-01
It is important to know the electric field in the tail current sheet in order to understand how particles behave and how much energy is being dissipated. The electric field is also a measurement of the reconnection rate during substorms. For the CDAW-6 substorm period of March 22, 1979, the authors used the ion data from the medium energy particles experiment (MEPE) on the ISEE-1 satellite, and studied nine measurements of the 3D distribution function centered on the center of the current sheet. The measured distribution function was then integrated to obtain the average of bulk flow velocity in the geocentric solar ecliptic (GSE) frame. This bulk flow velocity was then broken up into its components perpendicular and parallel to the magnetic field for the nine cases. It was further assumed that the perpendicular component was due, in part, to an energy dependent drift and to an energy independent electric field drift. Using the bulk flow velocities from any two energy channels they can separate out the electric and energy dependent drifts and thus obtain electric field and energy dependent components. The two lowest energy channels (34.3 keV and 54.9 keV) give the main results, and the 80.4 keV and 118.8 keV channels are used as a cross check. They find that E{sub x} fluctuates approximately {plus minus}5 mV/m, and E{sub y} {plus minus} 10 mV/m, in reasonable agreement with measurements by the electric field instrument, with most of the fluctuation presumably due to the motion of the current sheet. Using current sheet oscillation theory and the central current sheet data points, they can estimate E{sub y} in the frame of the current sheet and find a positive average E{sub y} with a magnitude of {approx} 0.1 mV/m, which is also consistent with that expected for reconnection in this substorm time period.
Optimization of Pathogen Capture in Flowing Fluids with Magnetic Nanoparticles.
Kang, Joo H; Um, Eujin; Diaz, Alexander; Driscoll, Harry; Rodas, Melissa J; Domansky, Karel; Watters, Alexander L; Super, Michael; Stone, Howard A; Ingber, Donald E
2015-11-11
Magnetic nanoparticles have been employed to capture pathogens for many biological applications; however, optimal particle sizes have been determined empirically in specific capturing protocols. Here, a theoretical model that simulates capture of bacteria is described and used to calculate bacterial collision frequencies and magnetophoretic properties for a range of particle sizes. The model predicts that particles with a diameter of 460 nm should produce optimal separation of bacteria in buffer flowing at 1 L h(-1) . Validating the predictive power of the model, Staphylococcus aureus is separated from buffer and blood flowing through magnetic capture devices using six different sizes of magnetic particles. Experimental magnetic separation in buffer conditions confirms that particles with a diameter closest to the predicted optimal particle size provide the most effective capture. Modeling the capturing process in plasma and blood by introducing empirical constants (ce ), which integrate the interfering effects of biological components on the binding kinetics of magnetic beads to bacteria, smaller beads with 50 nm diameters are predicted that exhibit maximum magnetic separation of bacteria from blood and experimentally validated this trend. The predictive power of the model suggests its utility for the future design of magnetic separation for diagnostic and therapeutic applications. PMID:26389806
Optimal flow sensor placement on wastewater treatment plants.
Villez, Kris; Vanrolleghem, Peter A; Corominas, Lluís
2016-09-15
Obtaining high quality data collected on wastewater treatment plants is gaining increasing attention in the wastewater engineering literature. Typical studies focus on recognition of faulty data with a given set of installed sensors on a wastewater treatment plant. Little attention is however given to how one can install sensors in such a way that fault detection and identification can be improved. In this work, we develop a method to obtain Pareto optimal sensor layouts in terms of cost, observability, and redundancy. Most importantly, the resulting method allows reducing the large set of possibilities to a minimal set of sensor layouts efficiently for any wastewater treatment plant on the basis of structural criteria only, with limited sensor information, and without prior data collection. In addition, the developed optimization scheme is fast. Practically important is that the number of sensors needed for both observability of all flows and redundancy of all flow sensors is only one more compared to the number of sensors needed for observability of all flows in the studied wastewater treatment plant configurations. PMID:27258618
NASA Astrophysics Data System (ADS)
Doyle, S. H.; Hubbard, A.
2015-12-01
Recent observations and modelling studies investigating the dynamic response of land-terminating regions of the Greenland ice sheet to a warmer climate remain at best unreconciled and at worst equivocal and contradictory. Some studies suggest that ice flow will be regulated over annual time scales by the development of efficient subglacial drainage. Others suggest that such self-regulation processes may not be effective at higher elevations and that the recent and projected expansion of supraglacial lakes further into the ice sheet interior has lead to increased ice flow at high elevations. On the other hand, the observation that rapid in situ supraglacial lake drainage events may be triggered by precursory basal motion have led to the argument that, by inference, such lake drainage in the interior may be impossible, or at least hindered, by reduced strain rates and lack of surface crevasses in these regions. The response of the Greenland ice sheet to a warmer, wetter climate, in which late summer and autumnal cyclonic weather events drive widespread melt, rainfall and transient accelerations may also need to be accounted for in assessments of future Greenland ice mass loss if predicted changes in Greenland's climate are realised. This talk will critically assess recent insights gained into this topic, attempt to resolve some of them, and suggest directions for future research.
NASA Astrophysics Data System (ADS)
Mishra, Sanjay; Yadava, Vinod
2013-06-01
The creation of small diameter holes in thin sheets (<3 mm) of superalloys using a laser beam is a challenging task. Knowledge of the effect of laser related process variables on hole related responses with respect to variation of sheet thickness is essential to obtain a hole of requisite quality. Therefore, in this paper a coupled methodology comprising of Finite Element Method (FEM) and Artificial Neural Network (ANN) has been used to develop a prediction model for the Laser Beam Percussion Drilling (LBPD) process. First, a 2D axisymmetric FEM-based thermal model for LBPD has been developed incorporating temperature-dependent thermal properties, optical properties and phase change phenomena of the sheet material. The developed FEM-based thermal model is validated with self-conducted experimental results in terms of hole taper which is further used to generate adequate input and output data for training and testing of the ANN model. Gray Relational Analysis (GRA) coupled with Principal Component Analysis (PCA) has been effectively used for the multi-objective optimization of the LBPD process utilizing the data predicted by the trained ANN model. The developed ANN model has been used to predict the performance characteristics of the LBPD process. The results predicted by the ANN model show that with the increase in pulse width and peak power the hole taper, material removal rate (MRR) and heat-affected zone (HAZ) increases. The acquired combination of optimal process variables produce a hole with good integral quality, i.e., a reduction of hole taper by 32.1%, increase of material removal rate by 28.9% and reduction of extent of HAZ by 4.5%.
NASA Astrophysics Data System (ADS)
Breuer, D.; Futterer, B.; Plesa, A.; Krebs, A.; Zaussinger, F.; Egbers, C.
2013-12-01
In mantle dynamics research, experiments, usually performed in rectangular geometries in Earth-based laboratories, have the character of ';exploring new physics and testing theories' [1]. In this work, we introduce our spherical geometry experiments on electro-hydrodynamical driven Rayleigh-Benard convection that have been performed for both temperature-independent (`GeoFlow I'), and temperature-dependent fluid viscosity properties (`GeoFlow II') with a measured viscosity contrast up to 1.5. To set up a self-gravitating force field, we use a high voltage potential between the inner and outer boundaries and a dielectric insulating liquid and perform the experiment under microgravity conditions at the ISS [2, 3]. Further, numerical simulations in 3D spherical geometry have been used to reproduce the results obtained in the `GeoFlow' experiments. For flow visualisation, we use Wollaston prism shearing interferometry which is an optical method producing fringe pattern images. Flow pattern differ between our two experiments (Fig. 1). In `GeoFlow I', we see a sheet-like thermal flow. In this case convection patterns have been successfully reproduced by 3D numerical simulations using two different and independently developed codes. In contrast, in `GeoFlow II' we obtain plume-like structures. Interestingly, numerical simulations do not yield this type of solution for the low viscosity contrast realised in the experiment. However, using a viscosity contrast of two orders of magnitude or higher, we can reproduce the patterns obtained in the `GeoFlow II' experiment, from which we conclude that non-linear effects shift the effective viscosity ratio [4]. References [1] A. Davaille and A. Limare (2009). In: Schubert, G., Bercovici, D. (Eds.), Treatise on Geophysics - Mantle Dynamics. [2] B. Futterer, C. Egbers, N. Dahley, S. Koch, L. Jehring (2010). Acta Astronautica 66, 193-100. [3] B. Futterer, N. Dahley, S. Koch, N. Scurtu, C. Egbers (2012). Acta Astronautica 71, 11-19. [4
Incorporating User Preferences Within an Optimal Traffic Flow Management Framework
NASA Technical Reports Server (NTRS)
Rios, Joseph Lucio; Sheth, Kapil S.; Guiterrez-Nolasco, Sebastian Armardo
2010-01-01
The effectiveness of future decision support tools for Traffic Flow Management in the National Airspace System will depend on two major factors: computational burden and collaboration. Previous research has focused separately on these two aspects without consideration of their interaction. In this paper, their explicit combination is examined. It is shown that when user preferences are incorporated with an optimal approach to scheduling, runtime is not adversely affected. A benefit-cost ratio is used to measure the influence of user preferences on an optimal solution. This metric shows user preferences can be accommodated without inordinately, negatively affecting the overall system delay. Specifically, incorporating user preferences will increase delays proportionally to increased user satisfaction.
Optimal Forebody Shape for Minimum Drag in Supersonic Flow
NASA Astrophysics Data System (ADS)
Natarajan, G.; Sahoo, N.; Kulkarni, V.
2015-01-01
In this work, a simple and efficient numerical approach to determine the shape of the minimum-drag axisymmetric forebody in inviscid supersonic flow with an attached shock constraint has been described. Taylor-Maccoll equation in conjunction with the tangent cone method is employed to estimate the pressure drag coefficient which is also chosen as the cost function. The forebody geometry is parameterized using a Non-Uniform Rational B-Splines (NURBS) curve whose control points are the design variables for optimisation using the steepest descent algorithm. Numerical studies demonstrate that the optimal forebody geometry for a given length and base radius has as much as 15 % lesser drag, depending on the Mach number than a cone of the same fineness ratio and that the convergence to the optimal solution exhibits a relatively weak Mach-number dependence.
NASA Astrophysics Data System (ADS)
Lavoie, C.; Domack, E. W.; Pettit, E. C.; Scambos, T. A.; Larter, R. D.; Schenke, H.-W.; Yoo, K. C.; Gutt, J.; Wellner, J.; Canals, M.; Anderson, J. B.; Amblas, D.
2014-10-01
We present a new seafloor map for the northern Antarctic Peninsula (AP), including swath multibeam data sets from five national programs. Our map allows for the examination and interpretation of Last Glacial Maximum (LGM) paleo-ice sheet/stream flow directions developed upon the seafloor from the preservation of: mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and accumulation centers (ice domes) on the AP continental shelf. The results show a flow bifurcation as ice exits the Larsen-B embayment. Flow emanating off the Seal Nunataks (including Robertson Island) is directed toward the southeast, then eastward as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" is directed toward the southeast then southward, as ice overflowed the tip of the Jason Peninsula to reach the southern perimeter of the embayment. Our reconstruction also refines the extent of at least five other distinct paleo-ice stream systems which, in turn, serve to delineate seven broad regions where contemporaneous ice domes must have been centered on the continental shelf during the LGM time interval. Our reconstruction is more detailed than other recent compilations because we followed specific flow indicators and have kept tributary flow paths parallel.
NASA Astrophysics Data System (ADS)
Ohtani, S.; Singer, H. J.; Mukai, T.
2006-01-01
The present study statistically examines how (or if) the geosynchronous (GOES) magnetic field responds to fast earthward flow observed by the Geotail satellite in the plasma sheet. The change of the GOES H (north-south) component within 15 min of the detection of fast flows, ΔH, is used as a primary measure of the geosynchronous response. It is found that following the detection of fast flows, the geosynchronous magnetic field rarely dipolarizes, but it often becomes more stretched, which is manifested by negative ΔH. This H decrease is not accompanied by any correlated variation of the D (azimuthal) component, suggesting that the associated stretching is not an edge effect of the substorm current wedge formation, but it can be attributed to the intensification of the local tail current. No systematic dependence of ΔH on the satellite separation can be found. On the other hand, the geosynchronous magnetic field tends to dipolarize if it is already stretched significantly, although the associated changes in the H and V (radial) components are not much larger than those in events that are not preconditioned. The flow intensity does not seem to be a controlling factor, either. However, caution needs to be exercised because the present study is not able to address the azimuthal structure of the fast flow. It is concluded that in most events the fast plasma flow does not reach geosynchronous orbit and that the generation of the fast plasma flow in the plasma sheet is not sufficient for causing geosynchronous dipolarization.
Kolmogorov spectrum consistent optimization for multi-scale flow decomposition
NASA Astrophysics Data System (ADS)
Mishra, M.; Liu, X.; Skote, M.; Fu, C.-W.
2014-05-01
Multi-scale analysis is widely adopted in turbulence research for studying flow structures corresponding to specific length scales in the Kolmogorov spectrum. In the present work, a new methodology based on novel optimization techniques for scale decomposition is introduced, which leads to a bandpass filter with prescribed properties. With this filter, we can efficiently perform scale decomposition using Fourier transform directly while adequately suppressing Gibbs ringing artifacts. Both 2D and 3D scale decomposition results are presented, together with qualitative and quantitative analysis. The comparison with existing multi-scale analysis technique is conducted to verify the effectiveness of our method. Validation of this decomposition technique is demonstrated both qualitatively and quantitatively. The advantage of the proposed methodology enables a precise specification of continuous length scales while preserving the original structures. These unique features of the proposed methodology may provide future insights into the evolution of turbulent flow structures.
Exact Convex Relaxation of Optimal Power Flow in Radial Networks
Gan, LW; Li, N; Topcu, U; Low, SH
2015-01-01
The optimal power flow (OPF) problem determines a network operating point that minimizes a certain objective such as generation cost or power loss. It is nonconvex. We prove that a global optimum of OPF can be obtained by solving a second-order cone program, under a mild condition after shrinking the OPF feasible set slightly, for radial power networks. The condition can be checked a priori, and holds for the IEEE 13, 34, 37, 123-bus networks and two real-world networks.
Limitations of Adjoint-Based Optimization for Separated Flows
NASA Astrophysics Data System (ADS)
Otero, J. Javier; Sharma, Ati; Sandberg, Richard
2015-11-01
Cabin noise is generated by the transmission of turbulent pressure fluctuations through a vibrating panel and can lead to fatigue. In the present study, we model this problem by using DNS to simulate the flow separating off a backward facing step and interacting with a plate downstream of the step. An adjoint formulation of the full compressible Navier-Stokes equations with varying viscosity is used to calculate the optimal control required to minimize the fluid-structure-acoustic interaction with the plate. To achieve noise reduction, a cost function in wavenumber space is chosen to minimize the excitation of the lower structural modes of the structure. To ensure the validity of time-averaged cost functions, it is essential that the time horizon is long enough to be a representative sample of the statistical behaviour of the flow field. The results from the current study show how this scenario is not always feasible for separated flows, because the chaotic behaviour of turbulence surpasses the ability of adjoint-based methods to compute time-dependent sensitivities of the flow.
NASA Astrophysics Data System (ADS)
Brücker, Ch.
1995-08-01
Scanning-Particle-Image-Velocimetry Technique (SPIV), introduced by Brücker (1992) and Brücker and Althaus (1992), offers the quantitative investigation of three-dimensional vortical structures in unsteady flows. On principle, this technique combines classical Particle-Image-Velocimetry (PIV) with volume scanning using a scanning light-sheet. In our previous studies, single scans obtained from photographic frame series were evaluated to show the instantaneous vortical structure of the respective flow phenomena. Here, continuous video recordings are processed to capture also the temporal information for the study of the set-up of 3D effects in the cylinder wake. The flow is continuously sampled in depth by the scanning light-sheet and in each of the parallel planes frame-to-frame cross-correlation of the video images (DPIV) is applied to obtain the 2D velocity field. Because the scanning frequency and repetition rate is high in comparison with the characteristic time-scale of the flow, the evaluation provides a complete time-record of the 3D flow during the starting process. With use of the continuity concept as described by Robinson and Rockwell (1993), we obtained in addition the out-of-plane component of the velocity in spanwise direction. This in view, the described technique enabled the reconstruction of the three-dimensional time-dependent velocity and vorticity field. The visualization of the dynamical behaviour of these quantities as, e.g. by video, gave a good impression of the spanwise flow showing the “tornado-like” suction effect of the starting vortices.
Optimizing the simulation of riverine species flow preferences
NASA Astrophysics Data System (ADS)
Kiesel, Jens; Pfannerstill, Matthias; Guse, Björn; Kakouei, Karan; Jähnig, Sonja C.; Fohrer, Nicola
2016-04-01
Riverine biota have distinct demands on the discharge regime. To quantify these demands, discharge time series are translated to ecohydrological indicators, e.g. magnitude, timing or duration of baseflow or peak flow events. These indicators are then related to species occurrence and/or absence to establish the feedback response of aquatic species to hydrological conditions. These links can be used in conjunction with hydrological simulations for predictions of species occurrences. If differences between observed and simulated ecohydrological indicator values are too high, such predictions can be wrong. Indicator differences can be due to poor input data quality and simplified model algorithms, but also depend on how the model was optimized. For instance, in case the model was optimised towards a single objective function, e.g. minimizing the difference between simulated and observed Q95, differences between simulated and observed high flow indicators will be smaller as compared to baseflow indicators. In this study, we are working towards assessing this error depending on the optimisation of the model. This assessment is based on a multi-objective vs. single-objective model optimization which we have realised in the following four-step approach: (1) sets of highly relevant ecohydrological indicators are defined; (2) the hydrologic model is optimised using a multi-objective function that combines all indicators; (3) the hydrologic model is optimised using single-objective functions with one optimisation round for each indicator and (4) the differences between all optimisation methods are calculated. By assessing these absolute (simulated vs observed) and relative (simulated vs simulated) differences, we can evaluate the magnitude of the possible error band when optimising a hydrological model towards different ecohydrological indicators. This assessment can be used to optimize hydrological models for depicting preferences of riverine biota more effectively and
Dynamic stochastic optimization models for air traffic flow management
NASA Astrophysics Data System (ADS)
Mukherjee, Avijit
This dissertation presents dynamic stochastic optimization models for Air Traffic Flow Management (ATFM) that enables decisions to adapt to new information on evolving capacities of National Airspace System (NAS) resources. Uncertainty is represented by a set of capacity scenarios, each depicting a particular time-varying capacity profile of NAS resources. We use the concept of a scenario tree in which multiple scenarios are possible initially. Scenarios are eliminated as possibilities in a succession of branching points, until the specific scenario that will be realized on a particular day is known. Thus the scenario tree branching provides updated information on evolving scenarios, and allows ATFM decisions to be re-addressed and revised. First, we propose a dynamic stochastic model for a single airport ground holding problem (SAGHP) that can be used for planning Ground Delay Programs (GDPs) when there is uncertainty about future airport arrival capacities. Ground delays of non-departed flights can be revised based on updated information from scenario tree branching. The problem is formulated so that a wide range of objective functions, including non-linear delay cost functions and functions that reflect equity concerns can be optimized. Furthermore, the model improves on existing practice by ensuring efficient use of available capacity without necessarily exempting long-haul flights. Following this, we present a methodology and optimization models that can be used for decentralized decision making by individual airlines in the GDP planning process, using the solutions from the stochastic dynamic SAGHP. Airlines are allowed to perform cancellations, and re-allocate slots to remaining flights by substitutions. We also present an optimization model that can be used by the FAA, after the airlines perform cancellation and substitutions, to re-utilize vacant arrival slots that are created due to cancellations. Finally, we present three stochastic integer programming
NASA Astrophysics Data System (ADS)
Abdul Hakeem, A. K.; Vishnu Ganesh, N.; Ganga, B.
2015-05-01
The magnetic field effect on a steady two dimensional laminar radiative flow of an incompressible viscous water based nanofluid over a stretching/shrinking sheet with second order slip boundary condition is investigated both analytically and numerically. The governing partial differential equations are reduced to nonlinear ordinary differential equations by means of Lie symmetry group transformations. The dimensionless governing equations for this investigation are solved analytically using hyper-geometric function and numerically by the fourth order Runge-Kutta method with the shooting technique. A unique exact solution exists for momentum equation in stretching sheet case and dual solutions are obtained for shrinking sheet case which has upper and lower branches. It is found that the lower branch solution vanishes in the presence of higher magnetic field. The velocity and temperature profiles, the local skin friction coefficient and the reduced Nusselt number are examined and discussed for different spherical nanoparticles such as Au, Ag, Cu, Al, Al2 O3 and TiO2. A comparative study between the previously published results and the present analytical and numerical results for a special case is found to be in good agreement.
NASA Astrophysics Data System (ADS)
Guo, Chengjie; Zheng, Liancun; Zhang, Chaoli; Chen, Xuehui; Zhang, Xinxin
2016-05-01
In this study, the generalised velocity slip and the generalised temperature jump of nanofluid in the flow over a stretching sheet with variable thickness are investigated. Because of the non-adherence of the fluid to a solid boundary, the velocity slip and the temperature jump between fluid and moving sheet may happen in industrial process, so taking velocity slip and temperature jump into account is indispensable. It is worth mentioning that the analysis of the velocity v, which has not been seen in the previous references related to the variable thickness sheet, is presented. The thermophoresis and the Brownian motion, which are the two very important physical parameters, are fully studied. The governing equations are simplified into ordinary differential equations by the proper transformations. The homotopy analysis method (HAM) is applied to solve the reduced equations for general conditions. In addition, the effects of involved parameters such as velocity slip parameter, temperature jump parameter, Prandtl number, magnetic field parameter, permeable parameter, Lewis number, thermophoresis parameter, and Brownian motion parameter are investigated and analysed graphically.
Accuracy improvement of the ice flow rate measurements on Antarctic ice sheet by DInSAR method
NASA Astrophysics Data System (ADS)
Shiramizu, Kaoru; Doi, Koichiro; Aoyama, Yuichi
2015-04-01
DInSAR (Differential Interferometric Synthetic Aperture Radar) is an effective tool to measure the flow rate of slow flowing ice streams on Antarctic ice sheet with high resolution. In the flow rate measurement by DInSAR method, we use Digital Elevation Model (DEM) at two times in the estimating process. At first, we use it to remove topographic fringes from InSAR images. And then, it is used to project obtained displacements along Line-Of-Sight (LOS) direction to the actual flow direction. ASTER-GDEM widely-used for InSAR prosessing of the data of polar region has a lot of errors especially in the inland ice sheet area. Thus the errors yield irregular flow rates and directions. Therefore, quality of DEM has a substantial influence on the ice flow rate measurement. In this study, we created a new DEM (resolution 10m; hereinafter referred to as PRISM-DEM) based on ALOS/PRISM images, and compared PRISM-DEM and ASTER-GDEM. The study area is around Skallen, 90km south from Syowa Station, in the southern part of Sôya Coast, East Antarctica. For making DInSAR images, we used ALOS/PALSAR data of 13 pairs (Path633, Row 571-572), observed during the period from November 23, 2007 through January 16, 2011. PRISM-DEM covering the PALSAR scene was created from nadir and backward view images of ALOS/PRISM (Observation date: 2009/1/18) by applying stereo processing with a digital mapping equipment, and then the automatically created a primary DEM was corrected manually to make a final DEM. The number of irregular values of actual ice flow rate was reduced by applying PRISM-DEM compared with that by applying ASTER-GDEM. Additionally, an averaged displacement of approximately 0.5cm was obtained by applying PRISM-DEM over outcrop area, where no crustal displacement considered to occur during the recurrence period of ALOS/PALSAR (46days), while an averaged displacement of approximately 1.65 cm was observed by applying ASTER-GDEM. Since displacements over outcrop area are considered
OPTIMIZATION OF COAL PARTICLE FLOW PATTERNS IN LOW NOX BURNERS
Jost O.L. Wendt; Gregory E. Ogden; Jennifer Sinclair; Stephanus Budilarto
2001-09-04
It is well understood that the stability of axial diffusion flames is dependent on the mixing behavior of the fuel and combustion air streams. Combustion aerodynamic texts typically describe flame stability and transitions from laminar diffusion flames to fully developed turbulent flames as a function of increasing jet velocity. Turbulent diffusion flame stability is greatly influenced by recirculation eddies that transport hot combustion gases back to the burner nozzle. This recirculation enhances mixing and heats the incoming gas streams. Models describing these recirculation eddies utilize conservation of momentum and mass assumptions. Increasing the mass flow rate of either fuel or combustion air increases both the jet velocity and momentum for a fixed burner configuration. Thus, differentiating between gas velocity and momentum is important when evaluating flame stability under various operating conditions. The research efforts described herein are part of an ongoing project directed at evaluating the effect of flame aerodynamics on NO{sub x} emissions from coal fired burners in a systematic manner. This research includes both experimental and modeling efforts being performed at the University of Arizona in collaboration with Purdue University. The objective of this effort is to develop rational design tools for optimizing low NO{sub x} burners. Experimental studies include both cold-and hot-flow evaluations of the following parameters: primary and secondary inlet air velocity, coal concentration in the primary air, coal particle size distribution and flame holder geometry. Hot-flow experiments will also evaluate the effect of wall temperature on burner performance.
Submarine landforms and ice-sheet flow in the Kvitøya Trough, northwestern Barents Sea
NASA Astrophysics Data System (ADS)
Hogan, K. A.; Dowdeswell, J. A.; Noormets, R.; Evans, J.; Cofaigh, C. Ó.; Jakobsson, M.
2010-12-01
High-resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in Kvitøya Trough, northwestern Barents Sea. A new swath-bathymetric dataset identifies three types of submarine landform in the study area (streamlined landforms, meltwater channels and cavities, iceberg scours). Subglacially produced streamlined landforms provide a record of ice flow through Kvitøya Trough during the last glaciation. Flow directions are inferred from the orientations of streamlined landforms (drumlins, crag-and-tail features). Ice flowed northward for at least 135 km from an ice divide at the southern end of Kvitøya Trough. A large channel-cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice-sheet base. Modest landform elongation ratios and a lack of mega-scale glacial lineations suggest that, although ice in Kvitøya Trough was melting at the bed and flowed faster than the likely thin and cold-based ice on adjacent banks, a major ice stream probably did not occupy the trough. Retreat was relatively rapid after 14-13.5 14C kyr B.P. and probably progressed via ice sheet-bed decoupling in response to rising sea level. There is little evidence for still stands during ice retreat or of ice-proximal deglacial sediments. Relict iceberg scours in present-day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat.
Optimal mixing and optimal stirring for fixed energy, fixed power, or fixed palenstrophy flows
NASA Astrophysics Data System (ADS)
Lunasin, Evelyn; Lin, Zhi; Novikov, Alexei; Mazzucato, Anna; Doering, Charles R.
2012-11-01
We consider passive scalar mixing by a prescribed divergence-free velocity vector field in a periodic box and address the following question: Starting from a given initial inhomogeneous distribution of passive tracers, and given a certain energy budget, power budget, or finite palenstrophy budget, what incompressible flow field best mixes the scalar quantity? We focus on the optimal stirring strategy recently proposed by Lin et al. ["Optimal stirring strategies for passive scalar mixing," J. Fluid Mech. 675, 465 (2011)], 10.1017/S0022112011000292 that determines the flow field that instantaneously maximizes the depletion of the H-1 mix-norm. In this work, we bridge some of the gap between the best available a priori analysis and simulation results. After recalling some previous analysis, we present an explicit example demonstrating finite-time perfect mixing with a finite energy constraint on the stirring flow. On the other hand, using a recent result by Wirosoetisno et al. ["Long time stability of a classical efficient scheme for two dimensional Navier-Stokes equations," SIAM J. Numer. Anal. 50(1), 126-150 (2012)], 10.1137/110834901 we establish that the H-1 mix-norm decays at most exponentially in time if the two-dimensional incompressible flow is constrained to have constant palenstrophy. Finite-time perfect mixing is thus ruled out when too much cost is incurred by small scale structures in the stirring. Direct numerical simulations in two dimensions suggest the impossibility of finite-time perfect mixing for flows with fixed power constraint and we conjecture an exponential lower bound on the H-1 mix-norm in this case. We also discuss some related problems from other areas of analysis that are similarly suggestive of an exponential lower bound for the H-1 mix-norm.
Optimal-Flow Minimum-Cost Correspondence Assignment in Particle Flow Tracking
Matov, Alexandre; Edvall, Marcus M.; Yang, Ge; Danuser, Gaudenz
2011-01-01
A diversity of tracking problems exists in which cohorts of densely packed particles move in an organized fashion, however the stability of individual particles within the cohort is low. Moreover, the flows of cohorts can regionally overlap. Together, these conditions yield a complex tracking scenario that can not be addressed by optical flow techniques that assume piecewise coherent flows, or by multiparticle tracking techniques that suffer from the local ambiguity in particle assignment. Here, we propose a graph-based assignment of particles in three consecutive frames to recover from image sequences the instantaneous organized motion of groups of particles, i.e. flows. The algorithm makes no a priori assumptions on the fraction of particles participating in organized movement, as this number continuously alters with the evolution of the flow fields in time. Graph-based assignment methods generally maximize the number of acceptable particles assignments between consecutive frames and only then minimize the association cost. In dense and unstable particle flow fields this approach produces many false positives. The here proposed approach avoids this via solution of a multi-objective optimization problem in which the number of assignments is maximized while their total association cost is minimized at the same time. The method is validated on standard benchmark data for particle tracking. In addition, we demonstrate its application to live cell microscopy where several large molecular populations with different behaviors are tracked. PMID:21720496
Zaimi, Khairy; Ishak, Anuar; Pop, Ioan
2014-01-01
The steady boundary layer flow and heat transfer of a nanofluid past a nonlinearly permeable stretching/shrinking sheet is numerically studied. The governing partial differential equations are reduced into a system of ordinary differential equations using a similarity transformation, which are then solved numerically using a shooting method. The local Nusselt number and the local Sherwood number and some samples of velocity, temperature and nanoparticle concentration profiles are graphically presented and discussed. Effects of the suction parameter, thermophoresis parameter, Brownian motion parameter and the stretching/shrinking parameter on the flow, concentration and heat transfer characteristics are thoroughly investigated. Dual solutions are found to exist in a certain range of the stretching/shrinking parameter for both shrinking and stretching cases. Results indicate that suction widens the range of the stretching/shrinking parameter for which the solution exists. PMID:24638147
Further developments in LP-based optimal power flow
Alsac, O.; Bright, J.; Prais, M.; Stott, B.P )
1990-08-01
Over the past twenty five years, the optimal power flow (OPF) approach that has received the most widespread practical application is the one based on linear programming (LP). Special customized LP methods have been utilized primarily for fast reliable security-constrained dispatch using decoupled separable OPF problem formulations. They have been used in power system planning, operations and control. Nevertheless, while the LP approach has a number of important attributes, its range of application in the OPF field has remained somewhat restricted. This paper describes further developments that have transformed the LP approach into a truly general-purpose OPF solver, with computational and other advantages over even recent nonlinear programming (NLP) methods. The nonseparable loss-minimization problem can now be solved, giving the same results as NLP on power systems of any size and type.
Optimal information provision for maximizing flow in a forked lattice
NASA Astrophysics Data System (ADS)
Imai, Takeaki; Nishinari, Katsuhiro
2015-06-01
In a forked road, the provision of inappropriate information to car drivers sometimes leads to undesirable situations such as one-sided congestion, which is called the hunting phenomenon in real traffic. To address such problems, we propose a forked exclusion model and investigate the behavior of traffic flow in two routes, providing various types of information to a limited number of traveling particles according to the share rate of information. To analytically understand the phenomena, we develop a coarse-grained representation of the model. By analyzing the model, we find the most effective types of information to minimize particles' travel time and the existence of an optimal share rate according to route conditions.
NASA Astrophysics Data System (ADS)
Camelbeeck, Thierry; Lombardi, Denis; Martin, Henri; Rapagnani, Giovanni
2015-04-01
The interactions of the Antarctic ice sheet with the various marginal orogenic belts is poorly understood. To make up for this lack of knowledge we installed in early 2014 in the Sør Rondane Mountains of eastern Queen Maud Land, five new broadband seismic stations, in addition to an existing permanent station setting up a 90 x 30 km wide seismic network. All stations are set up to be year-round autonomously powered, all but one being on rock outcrops. Despite technical problems encountered during winter, several months of data were collected and so far about 1 month of this dataset has been processed. The background seismic noise is found to be low to extremely low with seasonal variations suggesting influence from meteorological conditions. In addition to teleseismic events, a lot of local seismicity is observed and so far 155 local quakes were detected and localized using manual picking and 2 localization methods (Hypo and NonLinLoc). The inferred locations indicate 2 major source regions for these quakes: at the border between the ice sheet and outcropping mountains and within the fastest moving ice flow suggesting that the detected seismicity is correlated with the ice flow dynamics. Further information regarding the quake focal depths and the inferred crustal model will be discussed.
Zapp, F.C.; Thomas, O.W.; Silverman, M.D.; Dyslin, D.A.; Holmes, J.M.
1980-03-01
This study was undertaken at the request of the Fossil Fuel Processing Division of the Department of Energy. The report includes a compilation of conceptual flow sheets, including major equipment lists, and the results of an availability survey of potential suppliers of equipment associated with the coal and ash/slag operations that will be required by future large coal conversion plant complexes. Conversion plant flow sheet operations and related equipment requirements were based on two representative bituminous coals - Pittsburgh and Kentucky No. 9 - and on nine coal conversion processes. It appears that almost all coal handling and preparation and ash/slag removal equipment covered by this survey, with the exception of some coal comminution equipment, either is on hand or can readily be fabricated to meet coal conversion plant capacity requirements of up to 50,000 short tons per day. Equipment capable of handling even larger capacities can be developed. This approach appears to be unjustified, however, because in many cases a reasonable or optimum number of trains of equipment must be considered when designing a conversion plant complex. The actual number of trains of equipment selected will be influenced by the total requied capacity of the complex, the minimum on-line capacity that can be tolerated in case of equipment failure, reliability of specific equipment types, and the number of reactors and related feed injection stations needed for the specific conversion process.
Hamid, Rohana Abdul; Nazar, Roslinda; Pop, Ioan
2015-01-01
The paper deals with a stagnation-point boundary layer flow towards a permeable stretching/shrinking sheet in a nanofluid where the flow and the sheet are not aligned. We used the Buongiorno model that is based on the Brownian diffusion and thermophoresis to describe the nanofluid in this problem. The main purpose of the present paper is to examine whether the non-alignment function has the effect on the problem considered when the fluid suction and injection are imposed. It is interesting to note that the non-alignment function can ruin the symmetry of the flows and prominent in the shrinking sheet. The fluid suction will reduce the impact of the non-alignment function of the stagnation flow and the stretching/shrinking sheet but at the same time increasing the velocity profiles and the shear stress at the surface. Furthermore, the effects of the pertinent parameters such as the Brownian motion, thermophoresis, Lewis number and the suction/injection on the flow and heat transfer characteristics are also taken into consideration. The numerical results are shown in the tables and the figures. It is worth mentioning that dual solutions are found to exist for the shrinking sheet. PMID:26440761
NASA Astrophysics Data System (ADS)
Hamid, Rohana Abdul; Nazar, Roslinda; Pop, Ioan
2015-10-01
The paper deals with a stagnation-point boundary layer flow towards a permeable stretching/shrinking sheet in a nanofluid where the flow and the sheet are not aligned. We used the Buongiorno model that is based on the Brownian diffusion and thermophoresis to describe the nanofluid in this problem. The main purpose of the present paper is to examine whether the non-alignment function has the effect on the problem considered when the fluid suction and injection are imposed. It is interesting to note that the non-alignment function can ruin the symmetry of the flows and prominent in the shrinking sheet. The fluid suction will reduce the impact of the non-alignment function of the stagnation flow and the stretching/shrinking sheet but at the same time increasing the velocity profiles and the shear stress at the surface. Furthermore, the effects of the pertinent parameters such as the Brownian motion, thermophoresis, Lewis number and the suction/injection on the flow and heat transfer characteristics are also taken into consideration. The numerical results are shown in the tables and the figures. It is worth mentioning that dual solutions are found to exist for the shrinking sheet.
Pulsed pumping process optimization using a potential flow model.
Tenney, C M; Lastoskie, C M
2007-08-15
A computational model is applied to the optimization of pulsed pumping systems for efficient in situ remediation of groundwater contaminants. In the pulsed pumping mode of operation, periodic rather than continuous pumping is used. During the pump-off or trapping phase, natural gradient flow transports contaminated groundwater into a treatment zone surrounding a line of injection and extraction wells that transect the contaminant plume. Prior to breakthrough of the contaminated water from the treatment zone, the wells are activated and the pump-on or treatment phase ensues, wherein extracted water is augmented to stimulate pollutant degradation and recirculated for a sufficient period of time to achieve mandated levels of contaminant removal. An important design consideration in pulsed pumping groundwater remediation systems is the pumping schedule adopted to best minimize operational costs for the well grid while still satisfying treatment requirements. Using an analytic two-dimensional potential flow model, optimal pumping frequencies and pumping event durations have been investigated for a set of model aquifer-well systems with different well spacings and well-line lengths, and varying aquifer physical properties. The results for homogeneous systems with greater than five wells and moderate to high pumping rates are reduced to a single, dimensionless correlation. Results for heterogeneous systems are presented graphically in terms of dimensionless parameters to serve as an efficient tool for initial design and selection of the pumping regimen best suited for pulsed pumping operation for a particular well configuration and extraction rate. In the absence of significant retardation or degradation during the pump-off phase, average pumping rates for pulsed operation were found to be greater than the continuous pumping rate required to prevent contaminant breakthrough. PMID:17350717