NASA Astrophysics Data System (ADS)
Kravtsov, Alexander L.; Bobyleva, Elena V.; Grebenyukova, Tatyana P.; Kuznetsov, Oleg S.; Kulyash, Youri V.
2002-07-01
A quantitative flow microfluorometric method was used to study the intensity of human blood phagocyte degranulation in response to viable staphylococcus aureus or Yersinia pestis cells. Microorganisms were added directly to defibrinated whole blood. Uninfected and infected blood samples were incubated at 37 degrees C to 8 h. The results were recorded in dynamics after the staining of whole blood with acridine orange solution. Lymphocytes with a low azurophilic granule per cell content were discriminated from phagocytes by the measurement of single cell red cytoplasmic granule fluorescence. 30,000 cells in each sample were examined. S. aureus cells caused a dose-dependent decrease in the number of phagocytes having a high red cytoplasmic fluorescence intensity and a corresponding increase in the weakly fluorescence cell population. In the presence of an initial S. aureus-to-phagocyte ratio more than 1:1, degranulation was measured after 3 h of incubation and to 8 h the percentage of degranulated phagocytes was at least 100 percent Y. pestis cells grown for 48 h at 28 degrees C caused at same condition as the degranulation only about 50 percent of cells. Y.pestis EV cells preincubated in broth for 12 h at 37 degrees C did no stimulate the phahocyte degranulation. The results of these studies suggest that analysis of cell populations via flow microfluorimeter technology may be a powerful tool in analysis bacterial infection.
Geometry: A Flow Proof Approach.
ERIC Educational Resources Information Center
McMurray, Robert
The inspiration for this text was provided by an exposure to the flow proof approach to a proof format as opposed to the conventional two-column approach. Historical background is included, to provide a frame of reference to give the student an appreciation of the subject. The basic constructions are introduced early and briefly, to aid the…
Lattice Boltzmann approach for complex nonequilibrium flows.
Montessori, A; Prestininzi, P; La Rocca, M; Succi, S
2015-10-01
We present a lattice Boltzmann realization of Grad's extended hydrodynamic approach to nonequilibrium flows. This is achieved by using higher-order isotropic lattices coupled with a higher-order regularization procedure. The method is assessed for flow across parallel plates and three-dimensional flows in porous media, showing excellent agreement of the mass flow with analytical and numerical solutions of the Boltzmann equation across the full range of Knudsen numbers, from the hydrodynamic regime to ballistic motion.
Multidomain approach for calculating compressible flows
NASA Technical Reports Server (NTRS)
Cambier, L.; Chazzi, W.; Veuillot, J. P.; Viviand, H.
1982-01-01
A multidomain approach for calculating compressible flows by using unsteady or pseudo-unsteady methods is presented. This approach is based on a general technique of connecting together two domains in which hyperbolic systems (that may differ) are solved with the aid of compatibility relations associated with these systems. Some examples of this approach's application to calculating transonic flows in ideal fluids are shown, particularly the adjustment of shock waves. The approach is then applied to treating a shock/boundary layer interaction problem in a transonic channel.
Multigrid Approach to Incompressible Viscous Cavity Flows
NASA Technical Reports Server (NTRS)
Wood, William A.
1996-01-01
Two-dimensional incompressible viscous driven-cavity flows are computed for Reynolds numbers on the range 100-20,000 using a loosely coupled, implicit, second-order centrally-different scheme. Mesh sequencing and three-level V-cycle multigrid error smoothing are incorporated into the symmetric Gauss-Seidel time-integration algorithm. Parametrics on the numerical parameters are performed, achieving reductions in solution times by more than 60 percent with the full multigrid approach. Details of the circulation patterns are investigated in cavities of 2-to-1, 1-to-1, and 1-to-2 depth to width ratios.
Mixture modeling approach to flow cytometry data.
Boedigheimer, Michael J; Ferbas, John
2008-05-01
Flow Cytometry has become a mainstay technique for measuring fluorescent and physical attributes of single cells in a suspended mixture. These data are reduced during analysis using a manual or semiautomated process of gating. Despite the need to gate data for traditional analyses, it is well recognized that analyst-to-analyst variability can impact the dataset. Moreover, cells of interest can be inadvertently excluded from the gate, and relationships between collected variables may go unappreciated because they were not included in the original analysis plan. A multivariate non-gating technique was developed and implemented that accomplished the same goal as traditional gating while eliminating many weaknesses. The procedure was validated against traditional gating for analysis of circulating B cells in normal donors (n = 20) and persons with Systemic Lupus Erythematosus (n = 42). The method recapitulated relationships in the dataset while providing for an automated and objective assessment of the data. Flow cytometry analyses are amenable to automated analytical techniques that are not predicated on discrete operator-generated gates. Such alternative approaches can remove subjectivity in data analysis, improve efficiency and may ultimately enable construction of large bioinformatics data systems for more sophisticated approaches to hypothesis testing.
Lagrangian Flow Network approach to an open flow model
NASA Astrophysics Data System (ADS)
Ser-Giacomi, Enrico; Rodríguez-Méndez, Víctor; López, Cristóbal; Hernández-García, Emilio
2017-06-01
Concepts and tools from network theory, the so-called Lagrangian Flow Network framework, have been successfully used to obtain a coarse-grained description of transport by closed fluid flows. Here we explore the application of this methodology to open chaotic flows, and check it with numerical results for a model open flow, namely a jet with a localized wave perturbation. We find that network nodes with high values of out-degree and of finite-time entropy in the forward-in-time direction identify the location of the chaotic saddle and its stable manifold, whereas nodes with high in-degree and backwards finite-time entropy highlight the location of the saddle and its unstable manifold. The cyclic clustering coefficient, associated to the presence of periodic orbits, takes non-vanishing values at the location of the saddle itself.
PDF approach for compressible turbulent reacting flows
NASA Technical Reports Server (NTRS)
Hsu, A. T.; Tsai, Y.-L. P.; Raju, M. S.
1993-01-01
The objective of the present work is to develop a probability density function (pdf) turbulence model for compressible reacting flows for use with a CFD flow solver. The probability density function of the species mass fraction and enthalpy are obtained by solving a pdf evolution equation using a Monte Carlo scheme. The pdf solution procedure is coupled with a compressible CFD flow solver which provides the velocity and pressure fields. A modeled pdf equation for compressible flows, capable of capturing shock waves and suitable to the present coupling scheme, is proposed and tested. Convergence of the combined finite-volume Monte Carlo solution procedure is discussed, and an averaging procedure is developed to provide smooth Monte-Carlo solutions to ensure convergence. Two supersonic diffusion flames are studied using the proposed pdf model and the results are compared with experimental data; marked improvements over CFD solutions without pdf are observed. Preliminary applications of pdf to 3D flows are also reported.
A new numerical approach for compressible viscous flows
NASA Technical Reports Server (NTRS)
Wu, J. C.; Lekoudis, S. G.
1982-01-01
A numerical approach for computing unsteady compressible viscous flows was developed. This approach offers the capability of confining the region of computation to the viscous region of the flow. The viscous region is defined as the region where the vorticity is nonnegligible and the difference in dilatation between the potential flow and the real flow around the same geometry is also nonnegligible. The method was developed and tested. Also, an application of the procedure to the solution of the steady Navier-Stokes equations for incompressible internal flows is presented.
The pdf approach to turbulent flow
NASA Technical Reports Server (NTRS)
Kollmann, W.
1990-01-01
This paper provides a detailed discussion of the theory and application of probability density function (pdf) methods, which provide a complete statistical description of turbulent flow fields at a single point or a finite number of points. The basic laws governing the flow of Newtonian fluids are set up in the Eulerian and the Lagrangian frame, and the exact and linear equations for the characteristic functionals in those frames are discussed. Pdf equations in both frames are derived as Fourier transforms of the equations of the characteristic functions. Possible formulations for the nonclosed terms in the pdf equation are discussed, their properties are assessed, and closure modes for the molecular-transport and the fluctuating pressure-gradient terms are reviewed. The application of pdf methods to turbulent combustion flows, supersonic flows, and the interaction of turbulence with shock waves is discussed.
Validation of Modeling Flow Approaching Navigation Locks
2013-08-01
instrumentation, direction vernier . ........................................................................ 8 Figure 11. Plan A lock approach, upstream approach...13-9 8 Figure 9. Tools and instrumentation, bracket attached to rail. Figure 10. Tools and instrumentation, direction vernier . Numerical model
Parametric and experimental analysis using a power flow approach
NASA Technical Reports Server (NTRS)
Cuschieri, J. M.
1990-01-01
A structural power flow approach for the analysis of structure-borne transmission of vibrations is used to analyze the influence of structural parameters on transmitted power. The parametric analysis is also performed using the Statistical Energy Analysis approach and the results are compared with those obtained using the power flow approach. The advantages of structural power flow analysis are demonstrated by comparing the type of results that are obtained by the two analytical methods. Also, to demonstrate that the power flow results represent a direct physical parameter that can be measured on a typical structure, an experimental study of structural power flow is presented. This experimental study presents results for an L shaped beam for which an available solution was already obtained. Various methods to measure vibrational power flow are compared to study their advantages and disadvantages.
Combined AIE/EBE/GMRES approach to incompressible flows
NASA Astrophysics Data System (ADS)
Liou, J.; Tezduyar, T. E.
Adaptive implicit-explicit (AIE), grouped element-by-element (GEBE), and generalized minimum residuals (GMRES) solution techniques for incompressible flows are combined. In this approach, the GEBE and GMRES iteration methods are employed to solve the equation systems resulting from the implicitly treated elements, and therefore no direct solution effort is involved. The benchmarking results demonstrate that this approach can substantially reduce the CPU time and memory requirements in large-scale flow problems. Although the description of the concepts and the numerical demonstration are based on the incompressible flows, the approach presented here is applicable to larger class of problems in computational mechanics.
Magnetohydrodynamic equilibria with incompressible flows: Symmetry approach
Cicogna, G.; Pegoraro, F.
2015-02-15
We identify and discuss a family of azimuthally symmetric, incompressible, magnetohydrodynamic plasma equilibria with poloidal and toroidal flows in terms of solutions of the Generalized Grad Shafranov (GGS) equation. These solutions are derived by exploiting the incompressibility assumption, in order to rewrite the GGS equation in terms of a different dependent variable, and the continuous Lie symmetry properties of the resulting equation and, in particular, a special type of “weak” symmetries.
A Logical Approach to the Statement of Cash Flows
ERIC Educational Resources Information Center
Petro, Fred; Gean, Farrell
2014-01-01
Of the three financial statements in financial reporting, the Statement of Cash Flows (SCF) is perhaps the most challenging. The most difficult aspect of the SCF is in developing an understanding of how previous transactions are finalized in this document. The purpose of this paper is to logically explain the indirect approach of cash flow whereby…
Receptivity in parallel flows: An adjoint approach
NASA Technical Reports Server (NTRS)
Hill, D. Christopher
1993-01-01
Linear receptivity studies in parallel flows are aimed at understanding how external forcing couples to the natural unstable motions which a flow can support. The vibrating ribbon problem models the original Schubauer and Skramstad boundary layer experiment and represents the classic boundary layer receptivity problem. The process by which disturbances are initiated in convectively-unstable jets and shear layers has also received attention. Gaster was the first to handle the boundary layer analysis with the recognition that spatial modes, rather than temporal modes, were relevant when studying convectively-unstable flows that are driven by a time-harmonic source. The amplitude of the least stable spatial mode, far downstream of the source, is related to the source strength by a coupling coefficient. The determination of this coefficient is at the heart of this type of linear receptivity study. The first objective of the present study was to determine whether the various wave number derivative factors, appearing in the coupling coefficients for linear receptivity problems, could be reexpressed in a simpler form involving adjoint eigensolutions. Secondly, it was hoped that the general nature of this simplification could be shown; indeed, a rather elegant characterization of the receptivity properties of spatial instabilities does emerge. The analysis is quite distinct from the usual Fourier-inversion procedures, although a detailed knowledge of the spectrum of the Orr-Sommerfeld equation is still required. Since the cylinder wake analysis proved very useful in addressing control considerations, the final objective was to provide a foundation upon which boundary layer control theory may be developed.
Subsurface Flow and Transport: A Stochastic Approach
NASA Astrophysics Data System (ADS)
Desbarats, Alexandre
Anyone who has examined core or petrophysical logs from well bores has wondered at the rhythmic successions of sedimentary fades and has puzzled at their sudden disruption or reappearance. Such wonderment is no doubt shared by those who have stood at a quarry face gazing up at the intricate hierarchy of depositional patterns and the varied textures of sediments. A fortunate few have even slogged along a mine drift and observed at close hand the perplexing relationship between the geological fabric of a rock mass and occurrences of groundwater inflow. Happily, the heterogeneity of geological materials is now widely recognized and efforts over the last 20 years have been concerned with its incorporation into models of fluid flow and solute transport in the subsurface. These research efforts are, at least in part, driven by acute societal concerns over the contamination of groundwater resources and proposed plans for the disposal of nuclear and other toxic wastes in the subsurface.
Neural Flows in Hopfield Network Approach
NASA Astrophysics Data System (ADS)
Ionescu, Carmen; Panaitescu, Emilian; Stoicescu, Mihai
2013-12-01
In most of the applications involving neural networks, the main problem consists in finding an optimal procedure to reduce the real neuron to simpler models which still express the biological complexity but allow highlighting the main characteristics of the system. We effectively investigate a simple reduction procedure which leads from complex models of Hodgkin-Huxley type to very convenient binary models of Hopfield type. The reduction will allow to describe the neuron interconnections in a quite large network and to obtain information concerning its symmetry and stability. Both cases, on homogeneous voltage across the membrane and inhomogeneous voltage along the axon will be tackled out. Few numerical simulations of the neural flow based on the cable-equation will be also presented.
An active, collaborative approach to learning skills in flow cytometry.
Fuller, Kathryn; Linden, Matthew D; Lee-Pullen, Tracey; Fragall, Clayton; Erber, Wendy N; Röhrig, Kimberley J
2016-06-01
Advances in science education research have the potential to improve the way students learn to perform scientific interpretations and understand science concepts. We developed active, collaborative activities to teach skills in manipulating flow cytometry data using FlowJo software. Undergraduate students were given compensated clinical flow cytometry listmode output (FCS) files and asked to design a gating strategy to diagnose patients with different hematological malignancies on the basis of their immunophenotype. A separate cohort of research trainees was given uncompensated data files on which they performed their own compensation, calculated the antibody staining index, designed a sequential gating strategy, and quantified rare immune cell subsets. Student engagement, confidence, and perceptions of flow cytometry were assessed using a survey. Competency against the learning outcomes was assessed by asking students to undertake tasks that required understanding of flow cytometry dot plot data and gating sequences. The active, collaborative approach allowed students to achieve learning outcomes not previously possible with traditional teaching formats, for example, having students design their own gating strategy, without forgoing essential outcomes such as the interpretation of dot plots. In undergraduate students, favorable perceptions of flow cytometry as a field and as a potential career choice were correlated with student confidence but not the ability to perform flow cytometry data analysis. We demonstrate that this new pedagogical approach to teaching flow cytometry is beneficial for student understanding and interpretation of complex concepts. It should be considered as a useful new method for incorporating complex data analysis tasks such as flow cytometry into curricula.
NASA Astrophysics Data System (ADS)
Kondo, Makoto; Kuramata, Akito; Fujii, Takuya; Anayama, Chikashi; Okazaki, Jiro; Sekiguchi, Hiroshi; Tanahashi, Toshiyuki; Yamazaki, Susumu; Nakajima, Kazuo
1992-11-01
We present an approach to versatile highly-uniform MOVPE growth using the controlled stagnation point flow reactor. Our approach for uniform growth involves two concepts: (1) realizing the stagnation point flow condition in a vertical reactor configuration and (2) introducing a method for versatile flow-field control using the flow-controlled multiple gas-injector technique. The versatility of the flow-control technique was investigated by evaluating how radial deposition rate uniformity is affected by variation in several hydrodynamic and reactor configuration factors: the inlet flow rate, operating pressure, susceptor temperature, susceptor rotation speed, and the inlet and susceptor separation. We confirmed that a spatially uniform deposition rate can be obtained over a wide range of hydrodynamic and configuration parameters, demonstrating that the flow-control technique can provide a stable stagnation point flow field. Even when the ideal stagnation point flow-field is disturbed, for example, by high temperature susceptor heating, it could be completely compensated by adjusting the flow rate ratio for multiple injectors, showing our technique's ability to control flow-fields. By using this technique, we obtained excellent uniformities in both layer thickness and alloy composition for two important materials - GaInAsP and AlGaInP - in the same reactor.
A flow cytometric approach to quantify biofilms.
Kerstens, Monique; Boulet, Gaëlle; Van Kerckhoven, Marian; Clais, Sofie; Lanckacker, Ellen; Delputte, Peter; Maes, Louis; Cos, Paul
2015-07-01
Since biofilms are important in many clinical, industrial, and environmental settings, reliable methods to quantify these sessile microbial populations are crucial. Most of the currently available techniques do not allow the enumeration of the viable cell fraction within the biofilm and are often time consuming. This paper proposes flow cytometry (FCM) using the single-stain viability dye TO-PRO(®)-3 iodide as a fast and precise alternative. Mature biofilms of Candida albicans and Escherichia coli were used to optimize biofilm removal and dissociation, as a single-cell suspension is needed for accurate FCM enumeration. To assess the feasibility of FCM quantification of biofilms, E. coli and C. albicans biofilms were analyzed using FCM and crystal violet staining at different time points. A combination of scraping and rinsing proved to be the most efficient technique for biofilm removal. Sonicating for 10 min eliminated the remaining aggregates, resulting in a single-cell suspension. Repeated FCM measurements of biofilm samples revealed a good intraday precision of approximately 5 %. FCM quantification and the crystal violet assay yielded similar biofilm growth curves for both microorganisms, confirming the applicability of our technique. These results show that FCM using TO-PRO(®)-3 iodide as a single-stain viability dye is a valid fast alternative for the quantification of viable cells in a biofilm.
Parametric and experimental analysis using a power flow approach
NASA Technical Reports Server (NTRS)
Cuschieri, J. M.
1988-01-01
Having defined and developed a structural power flow approach for the analysis of structure-borne transmission of structural vibrations, the technique is used to perform an analysis of the influence of structural parameters on the transmitted energy. As a base for comparison, the parametric analysis is first performed using a Statistical Energy Analysis approach and the results compared with those obtained using the power flow approach. The advantages of using structural power flow are thus demonstrated by comparing the type of results obtained by the two methods. Additionally, to demonstrate the advantages of using the power flow method and to show that the power flow results represent a direct physical parameter that can be measured on a typical structure, an experimental investigation of structural power flow is also presented. Results are presented for an L-shaped beam for which an analytical solution has already been obtained. Furthermore, the various methods available to measure vibrational power flow are compared to investigate the advantages and disadvantages of each method.
Steady shear flow thermodynamics based on a canonical distribution approach.
Taniguchi, Tooru; Morriss, Gary P
2004-11-01
A nonequilibrium steady-state thermodynamics to describe shear flow is developed using a canonical distribution approach. We construct a canonical distribution for shear flow based on the energy in the moving frame using the Lagrangian formalism of the classical mechanics. From this distribution, we derive the Evans-Hanley shear flow thermodynamics, which is characterized by the first law of thermodynamics dE=TdS-Qdgamma relating infinitesimal changes in energy E, entropy S, and shear rate gamma with kinetic temperature T. Our central result is that the coefficient Q is given by Helfand's moment for viscosity. This approach leads to thermodynamic stability conditions for shear flow, one of which is equivalent to the positivity of the correlation function for Q. We show the consistency of this approach with the Kawasaki distribution function for shear flow, from which a response formula for viscosity is derived in the form of a correlation function for the time-derivative of Q. We emphasize the role of the external work required to sustain the steady shear flow in this approach, and show theoretically that the ensemble average of its power W must be non-negative. A nonequilibrium entropy, increasing in time, is introduced, so that the amount of heat based on this entropy is equal to the average of W. Numerical results from nonequilibrium molecular-dynamics simulation of two-dimensional many-particle systems with soft-core interactions are presented which support our interpretation.
A geometric approach to the analysis of physiological flow data.
Shih, W J
1994-02-15
Physiological flow data are common in various medical fields. Examples include urinary, blood and expiratory flows. They are widely used in assessing functions in the urinary, circulatory, or pulmonary systems, respectively. Current statistical methods for analysing these flow data in clinical trials are either univariate analyses, which do not utilize all the information together, or some conventional multivariate methods (such as regression analyses) which yield results that do not render clear medical interpretations. This paper presents a new approach to analysing the flow data, using urinary flow as the primary focus. The basic idea and technical steps are applicable to other flow data as well. The proposed method aims to transform the flow measurements back to the shape of the flow graphs. Since the whole geometric pattern of the flow graph provides more information about the patient's flow condition than any individual flow parameter alone, the method is a meaningful way of combining and analysing the flow data in both statistical and clinical senses. The method is a three-stage procedure. Patients are classified into three classes in the first stage and then ranked in sequence in the second stage, according to the geometry of the shape pattern and some clinical criteria. The classification procedure is shown to be very reliable when compared with the clinician's visual evaluation, and hence can be implemented by computer programming to aid clinical trials involving many patients. The whole ranking score is then readily analysed at the third stage for comparing treatment effects by the analysis of covariance method based on ranks, with the post-treatment score as the response variable and the baseline score as the covariate. An example of a urinary flow data set is provided to illustrate the use of the procedure.
Hydrokinetic approach to large-scale cardiovascular blood flow
NASA Astrophysics Data System (ADS)
Melchionna, Simone; Bernaschi, Massimo; Succi, Sauro; Kaxiras, Efthimios; Rybicki, Frank J.; Mitsouras, Dimitris; Coskun, Ahmet U.; Feldman, Charles L.
2010-03-01
We present a computational method for commodity hardware-based clinical cardiovascular diagnosis based on accurate simulation of cardiovascular blood flow. Our approach leverages the flexibility of the Lattice Boltzmann method to implementation on high-performance, commodity hardware, such as Graphical Processing Units. We developed the procedure for the analysis of real-life cardiovascular blood flow case studies, namely, anatomic data acquisition, geometry and mesh generation, flow simulation and data analysis and visualization. We demonstrate the usefulness of our computational tool through a set of large-scale simulations of the flow patterns associated with the arterial tree of a patient which involves two hundred million computational cells. The simulations show evidence of a very rich and heterogeneous endothelial shear stress pattern (ESS), a quantity of recognized key relevance to the localization and progression of major cardiovascular diseases, such as atherosclerosis, and set the stage for future studies involving pulsatile flows.
Assessment of BGK Approaches to Modeling of Nozzle Flows (PREPRINT)
2009-10-07
5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) R. Kumar, E.V. Titov , and D.A. Levin (Penn State); N.E. Gimelshein and S.F. 5d...Assessment of BGK Approaches to Modeling of Nozzle Flows in the Near Continuum Regime Rakesh Kumar∗, E. V. Titov † and D.A. Levin‡ Pennsylvania State
A perturbation-theoretic approach to Lagrangian flow networks
NASA Astrophysics Data System (ADS)
Fujiwara, Naoya; Kirchen, Kathrin; Donges, Jonathan F.; Donner, Reik V.
2017-03-01
Complex network approaches have been successfully applied for studying transport processes in complex systems ranging from road, railway, or airline infrastructures over industrial manufacturing to fluid dynamics. Here, we utilize a generic framework for describing the dynamics of geophysical flows such as ocean currents or atmospheric wind fields in terms of Lagrangian flow networks. In this approach, information on the passive advection of particles is transformed into a Markov chain based on transition probabilities of particles between the volume elements of a given partition of space for a fixed time step. We employ perturbation-theoretic methods to investigate the effects of modifications of transport processes in the underlying flow for three different problem classes: efficient absorption (corresponding to particle trapping or leaking), constant input of particles (with additional source terms modeling, e.g., localized contamination), and shifts of the steady state under probability mass conservation (as arising if the background flow is perturbed itself). Our results demonstrate that in all three cases, changes to the steady state solution can be analytically expressed in terms of the eigensystem of the unperturbed flow and the perturbation itself. These results are potentially relevant for developing more efficient strategies for coping with contaminations of fluid or gaseous media such as ocean and atmosphere by oil spills, radioactive substances, non-reactive chemicals, or volcanic aerosols.
Computational approach for probing the flow through artificial heart devices.
Kiris, C; Kwak, D; Rogers, S; Chang, I D
1997-11-01
Computational fluid dynamics (CFD) has become an indispensable part of aerospace research and design. The solution procedure for incompressible Navier-Stokes equations can be used for biofluid mechanics research. The computational approach provides detailed knowledge of the flowfield complementary to that obtained by experimental measurements. This paper illustrates the extension of CFD techniques to artificial heart flow simulation. Unsteady incompressible Navier-Stokes equations written in three-dimensional generalized curvilinear coordinates are solved iteratively at each physical time step until the incompressibility condition is satisfied. The solution method is based on the pseudocompressibility approach. It uses an implicit upwind-differencing scheme together with the Gauss-Seidel line-relaxation method. The efficiency and robustness of the time-accurate formulation of the numerical algorithm are tested by computing the flow through model geometries. A channel flow with a moving indentation is computed and validated by experimental measurements and other numerical solutions. In order to handle the geometric complexity and the moving boundary problems, a zonal method and an overlapped grid embedding scheme are employed, respectively. Steady-state solutions for the flow through a tilting-disk heart valve are compared with experimental measurements. Good agreement is obtained. Aided by experimental data, the flow through an entire Penn State artificial heart model is computed.
A Galerkin least squares approach to viscoelastic flow.
Rao, Rekha R.; Schunk, Peter Randall
2015-10-01
A Galerkin/least-squares stabilization technique is applied to a discrete Elastic Viscous Stress Splitting formulation of for viscoelastic flow. From this, a possible viscoelastic stabilization method is proposed. This method is tested with the flow of an Oldroyd-B fluid past a rigid cylinder, where it is found to produce inaccurate drag coefficients. Furthermore, it fails for relatively low Weissenberg number indicating it is not suited for use as a general algorithm. In addition, a decoupled approach is used as a way separating the constitutive equation from the rest of the system. A Pressure Poisson equation is used when the velocity and pressure are sought to be decoupled, but this fails to produce a solution when inflow/outflow boundaries are considered. However, a coupled pressure-velocity equation with a decoupled constitutive equation is successful for the flow past a rigid cylinder and seems to be suitable as a general-use algorithm.
A novel approach for Doppler blood flow measurement.
McNamara, D M; Goli, A; Ziarani, A K
2008-01-01
A new approach to frequency estimation for the velocity estimation in Doppler ultrasound blood flow analysis is presented. The basis of the approach is an adaptive sinusoid-tracking algorithm which is effective in extracting nonstationary signals from within noise and estimating their time-varying parameters, such as the frequency, over time. The preliminary studies conducted using simulated signals show the potential of this approach in estimating Doppler frequency shifts under noisy conditions. A qualitative comparison with the short-time Fourier transform (STFT) is presented to show the advantages of the proposed technique over the STFT. The proposed approach offers advantages over conventional time-frequency analysis techniques in terms of high time-frequency resolution and high noise immunity.
A probabilistic approach to modeling and controlling fluid flows
NASA Astrophysics Data System (ADS)
Kaiser, Eurika; Noack, Bernd R.; Spohn, Andreas; Cattafesta, Louis N.; Morzynski, Marek; Daviller, Guillaume; Brunton, Bingni W.; Brunton, Steven L.
2016-11-01
We extend cluster-based reduced-order modeling (CROM) (Kaiser et al., 2014) to include control inputs in order to determine optimal control laws with respect to a cost function for unsteady flows. The proposed methodology frames high-dimensional, nonlinear dynamics into low- dimensional, probabilistic, linear dynamics which considerably simplifies the optimal control problem while preserving nonlinear actuation mechanisms. The data-driven approach builds upon the unsupervised partitioning of the data into few kinematically similar flow states using a clustering algorithm. The coarse-grained dynamics are then described by a Markov model which is closely related to the approximation of Perron-Frobenius operators. The Markov model can be used as predictor for the ergodic probability distribution for a particular control law approximating the long-term behavior of the system on which basis the optimal control law is determined. Moreover, we combine CROM with a recently developed approach for optimal sparse sensor placement for classification (Brunton et al., 2013) as a critical enabler for in-time control and for the systematic identification of dynamical regimes from few measurements. The approach is applied to a separating flow and a mixing layer exhibiting vortex pairing.
A Shallow Layer Approach for Geo-flow emplacement
NASA Astrophysics Data System (ADS)
Costa, A.; Folch, A.; Mecedonio, G.
2009-04-01
Geophysical flows such as lahars or lava flows severely threat the communities located on or near the volcano flanks. Risks and damages caused by the propagation of this kind of flows require a quantitative description of this phenomenon and reliable tools for forecasting their emplacement. Computational models are a valuable tool for planning risk mitigation countermeasures, such as human intervention to force flow diversion, artificial barriers, and allow for significant economical and social benefits. A FORTRAN 90 code based on a Shallow Layer Approach for Geo-flows (SLAG) for describing transport and emplacement of diluted lahars, water and lava was developed in both serial and parallel version. Three rheological models, such as those describing i) a viscous, ii) a turbulent, and iii) a dilatant flow respectively, were implemented in order to describe transport of lavas, water and diluted lahars. The code was made user-friendly by creating some interfaces that allow the user to easily define the problem, extract and interpolate the topography of the simulation domain. Moreover SLAG outputs can be written in both GRD format (e.g., Surfer), NetCDF format, or visualized directly in GoogleEarth. In SLAG the governing equations were treated using a Godunov splitting method following George (2008) algorithm based on a Riemann solver for the shallow water equations that decomposes an augmented state variable the depth, momentum, momentum flux, and bathymetry into four propagating discontinuities or waves. For our application, the algorithm was generalized for solving the energy equation. For validating the code in simulating real geophysical flows, we performed few simulations the lava flow event of the the 3rd and 4th January 1992 Etna eruption, the July 2001 Etna lava flows, January 2002 Nyragongo lava flows and few test cases for simulating transport of diluted lahars. Ref: George, D.L. (2008), Augmented Riemann Solvers for the Shallow Water Equations over Variable
A conservative approach for flow field calculations on multiple grids
NASA Technical Reports Server (NTRS)
Kathong, Monchai; Tiwari, Surendra N.
1988-01-01
In the computation of flow fields about complex configurations, it is very difficult to construct body-fitted coordinate systems. An alternative approach is to use several grids at once, each of which is generated independently. This procedure is called the multiple grids or zonal grids approach and its applications are investigated in this study. The method follows the conservative approach and provides conservation of fluxes at grid interfaces. The Euler equations are solved numerically on such grids for various configurations. The numerical scheme used is the finite-volume technique with a three-state Runge-Kutta time integration. The code is vectorized and programmed to run on the CDC VPS-32 computer. Some steady state solutions of the Euler equations are presented and discussed.
A hybrid particle/continuum approach for nonequilibrium hypersonic flows
NASA Astrophysics Data System (ADS)
Wang, Wen-Lan
A hybrid particle-continuum computational framework is developed and presented for simulating nonequilibrium hypersonic flows, aimed to be more accurate than conventional continuum methods and faster than particle methods. The frame work consists of the direct simulation Monte Carlo-Information Preservation (DSMC-IP) method coupled with a Navier-Stokes solver. Since the DSMC-IP method provides the macroscopic information at each time step, determination of the continuum fluxes across the interface between the particle and continuum domains becomes straightforward. Buffer and reservoir calls are introduced in the continuum domain and work as an extension of the particle domain. At the end of the particle movement phase, particles in either particle or buffer cells are retained. All simulated particles in the reservoir cells are first deleted for each time, step and re-generated based on the local cell values. The microscopic velocities for the newly generated particles are initialized to the Chapman-Enskog distribution using an acceptance-rejection scheme. Continuum breakdown in a flow is defined as when the continuum solution departs from the particle solution to at least 5%. Numerical investigations show that a Knudsen-number-like parameter can best predict the continuum breakdown in the flows of interest. Numerical experiments of hypersonic flows over a simple blunted cone and a much more complex hollow cylinder/flare are conducted. The solutions for the two geometries considered from the hybrid framework are compared with experimental data and pure particle solutions. Generally speaking, it is concluded that the hybrid approach works quite well. In the blunted cone flow, numerical accuracy is improved when 10 layers of buffer cells are employed and the continuum breakdown cut-off value is set to be 0.03. In the hollow cylinder/flare hybrid simulation, the size of the separation zone near the conjunction of the cylinder and flare is improved from the initial
Characterising powder flow properties - the need for a multivariate approach
NASA Astrophysics Data System (ADS)
Freeman, Tim; Brockbank, Katrina; Sabathier, Jerome
2017-06-01
Despite their widespread and well-established use, powders are challenging materials to work with, as evidenced by the common problems encountered during storage and processing, as well as in the quality and consistency of final products. The diverse range of unit operations used to handle and manipulate powders subject them to extremes of stress and flow regimes; from the high stress, static conditions present in hoppers to the dispersed, dynamic state of a fluidised bed dryer. It is therefore possible for a powder to behave a certain way in a given unit operation, but entirely differently in another. Many existing powder testing techniques don't deliver the required information as the test conditions do not represent the conditions in the process. Modern powder rheometers generate process relevant data by accurately measuring dynamic flow, bulk and shear properties. This approach enables a powder's response to aeration, consolidation, forced flow and changes in flow rate to be reliably quantified thereby simulating the conditions which a powder will be subjected to in process. This paper provides an introduction to powder rheology, including a comparison with traditional techniques, and uses case studies to demonstrate how powder rheology can be applied to optimise production processes and enhance product quality
A hydrometeorological forecasting approach for basins with complex flow regime
NASA Astrophysics Data System (ADS)
Zarkadoulas, Akis; Mantesi, Konstantina; Efstratiadis, Andreas; Koussis, Antonis; Mazi, Aikaterini; Katsanos, Demetris; Koukouvinos, Antonis; Koutsoyiannis, Demetris
2015-04-01
The combined use of weather forecasting models and hydrological models in flood risk estimations is an established technique, with several successful applications worldwide. However, most known hydrometeorological forecasting systems have been established in large rivers with perpetual flow. Experience from small- and medium-scale basins, which are often affected by flash floods, is very limited. In this work we investigate the perspectives of hydrometeorological forecasting, by emphasizing two issues: (a) which modelling approach can credibly represent the complex dynamics of basins with highly variable runoff (intermittent or ephemeral); and (b) which transformation of point-precipitation forecasts provides the most reliable estimations of spatially aggregated data, to be used as inputs to semi-distributed hydrological models. Using as case studies the Sarantapotamos river basin, in Eastern Greece (145 km2), and the Nedontas river basin, in SW Peloponnese (120 km2), we demonstrate the advantages of continuous simulation through the HYDROGEIOS model. This employs conjunctive modelling of surface and groundwater flows and their interactions (percolation, infiltration, underground losses), which are key processes in river basins characterized by significantly variability of runoff. The model was calibrated against hourly flow data at two and three hydrometric stations, respectively, for a 3-year period (2011-2014). Next we attempted to reproduce the most intense flood events of that period, by substituting observed rainfall by forecast scenarios. In this respect, we used consecutive point forecasts of a 6-hour lead time, provided by the numerical weather prediction model WRF (Advanced Research version), dynamically downscaled from the ~1° forecast of GSF-NCEP/NOAA successively first to ~18 km, then to ~6 km and ultimately at the horizontal grid resolution of 2x2 km2. We examined alternative spatial integration approaches, using as reference the rainfall stations
Approaches to the simulation of unconfined flow and perched groundwater flow in MODFLOW.
Bedekar, Vivek; Niswonger, Richard G; Kipp, Kenneth; Panday, Sorab; Tonkin, Matthew
2012-01-01
Various approaches have been proposed to manage the nonlinearities associated with the unconfined flow equation and to simulate perched groundwater conditions using the MODFLOW family of codes. The approaches comprise a variety of numerical techniques to prevent dry cells from becoming inactive and to achieve a stable solution focused on formulations of the unconfined, partially-saturated, groundwater flow equation. Keeping dry cells active avoids a discontinuous head solution which in turn improves the effectiveness of parameter estimation software that relies on continuous derivatives. Most approaches implement an upstream weighting of intercell conductance and Newton-Raphson linearization to obtain robust convergence. In this study, several published approaches were implemented in a stepwise manner into MODFLOW for comparative analysis. First, a comparative analysis of the methods is presented using synthetic examples that create convergence issues or difficulty in handling perched conditions with the more common dry-cell simulation capabilities of MODFLOW. Next, a field-scale three-dimensional simulation is presented to examine the stability and performance of the discussed approaches in larger, practical, simulation settings.
Approaches to the simulation of unconfined flow and perched groundwater flow in MODFLOW
Bedekar, Vivek; Niswonger, Richard G.; Kipp, Kenneth; Panday, Sorab; Tonkin, Matthew
2012-01-01
Various approaches have been proposed to manage the nonlinearities associated with the unconfined flow equation and to simulate perched groundwater conditions using the MODFLOW family of codes. The approaches comprise a variety of numerical techniques to prevent dry cells from becoming inactive and to achieve a stable solution focused on formulations of the unconfined, partially-saturated, groundwater flow equation. Keeping dry cells active avoids a discontinuous head solution which in turn improves the effectiveness of parameter estimation software that relies on continuous derivatives. Most approaches implement an upstream weighting of intercell conductance and Newton-Raphson linearization to obtain robust convergence. In this study, several published approaches were implemented in a stepwise manner into MODFLOW for comparative analysis. First, a comparative analysis of the methods is presented using synthetic examples that create convergence issues or difficulty in handling perched conditions with the more common dry-cell simulation capabilities of MODFLOW. Next, a field-scale three-dimensional simulation is presented to examine the stability and performance of the discussed approaches in larger, practical, simulation settings.
A methodological approach of estimating resistance to flow under unsteady flow conditions
NASA Astrophysics Data System (ADS)
Mrokowska, M. M.; Rowiński, P. M.; Kalinowska, M. B.
2015-10-01
This paper presents an evaluation and analysis of resistance parameters: friction slope, friction velocity and Manning coefficient in unsteady flow. The methodology to enhance the evaluation of resistance by relations derived from flow equations is proposed. The main points of the methodology are (1) to choose a resistance relation with regard to a shape of a channel and (2) type of wave, (3) to choose an appropriate method to evaluate slope of water depth, and (4) to assess the uncertainty of result. In addition to a critical analysis of existing methods, new approaches are presented: formulae for resistance parameters for a trapezoidal channel, and a translation method instead of Jones' formula to evaluate the gradient of flow depth. Measurements obtained from artificial dam-break flood waves in a small lowland watercourse have made it possible to apply the method and to analyse to what extent resistance parameters vary in unsteady flow. The study demonstrates that results of friction slope and friction velocity are more sensitive to applying simplified formulae than the Manning coefficient (n). n is adequate as a flood routing parameter but may be misleading when information on trend of resistance with flow rate is crucial. Then friction slope or friction velocity seems to be better choice.
Compositional Space Parameterization Approach for Reservoir Flow Simulation
NASA Astrophysics Data System (ADS)
Voskov, D.
2011-12-01
Phase equilibrium calculations are the most challenging part of a compositional flow simulation. For every gridblock and at every time step, the number of phases and their compositions must be computed for the given overall composition, temperature, and pressure conditions. The conventional approach used in petroleum industry is based on performing a phase-stability test, and solving the fugacity constraints together with the coupled nonlinear flow equations when the gridblock has more than one phase. The multi-phase compositional space can be parameterized in terms of tie-simplexes. For example, a tie-triangle can be used such that its interior encloses the three-phase region, and the edges represent the boundary with specific two-phase regions. The tie-simplex parameterization can be performed for pressure, temperature, and overall composition. The challenge is that all of these parameters can change considerably during the course of a simulation. It is possible to prove that the tie-simplexes change continuously with respect to pressure, temperature, and overall composition. The continuity of the tie-simplex parameterization allows for interpolation using discrete representations of the tie-simplex space. For variations of composition, a projection to the nearest tie-simplex is used, and if the tie-simplex is within a predefined tolerance, it can be used directly to identify the phase-state of this composition. In general, our parameterization approach can be seen as the generalization of negative flash idea for systems with two or more phases. Theory of dispersion-free compositional displacements, as well as computational experience of general-purpose compositional flow simulation indicates that the displacement path in compositional space is determined by a limited number of tie-simplexes. Therefore, only few tie-simplex tables are required to parameterize the entire displacement. The small number of tie-simplexes needed in a course of a simulation motivates
Cryogenic parallel, single phase flows: an analytical approach
NASA Astrophysics Data System (ADS)
Eichhorn, R.
2017-02-01
Managing the cryogenic flows inside a state-of-the-art accelerator cryomodule has become a demanding endeavour: In order to build highly efficient modules, all heat transfers are usually intercepted at various temperatures. For a multi-cavity module, operated at 1.8 K, this requires intercepts at 4 K and at 80 K at different locations with sometimes strongly varying heat loads which for simplicity reasons are operated in parallel. This contribution will describe an analytical approach, based on optimization theories.
Transformation approaches for simulating flow in variably saturated porous media
NASA Astrophysics Data System (ADS)
Williams, Glenn A.; Miller, Cass T.; Kelley, C. T.
2000-04-01
Sharp fronts with rapid changes in fluid saturations over short distance and timescales often exist in multiphase flow in subsurface systems. Such highly nonlinear problems are notoriously difficult to solve, and standard solution approaches are often inefficient and unreliable. We summarize four existing and one new transformation method (IT2) for solving Richards'; equation within a common framework and compare performance for a range of medium properties and simulation conditions. The new IT2 transform is defined as a linear combination of volumetric water fraction of the aqueous phase and integrated hydraulic conductivity terms. We show that transformation methods can significantly improve solution efficiency and robustness compared to standard solution approaches; optimal transformation parameters depend upon auxiliary conditions, medium properties, and spatial and temporal discretization and are difficult to evaluate a priori; and IT2 compares favorably with existing transforms.
A Potential Approach for Low Flow Selection in Water Resource Supply and Management
Ying Ouyang
2012-01-01
Low flow selections are essential to water resource management, water supply planning, and watershed ecosystem restoration. In this study, a new approach, namely the frequent-low (FL) approach (or frequent-low index), was developed based on the minimum frequent-low flow or level used in minimum flows and/or levels program in northeast Florida, USA. This FL approach was...
Dai, Xiwen; Aurégan, Yves
2016-09-01
The effect of a shear flow on an acoustic liner consisting of a perforated plate backed by cavities is studied. Two different approaches are investigated: First, the duct and the liner are considered as a periodic system while in the second approach the liner is considered as homogeneous and described by an impedance. Those two approaches coincide perfectly without flow for a small hole spacing compared to the acoustic wavelength. This work demonstrates that those two approaches are not wholly consistent when a shear flow is present and reveals some problems in the use of the local impedance with flow. The no-flow impedance cannot be used to describe the liner when a shear flow is present. An equivalent impedance with flow can be defined but it depends on the direction of the incident waves and loses its local characteristic.
Solving the power flow equations: a monotone operator approach
Dvijotham, Krishnamurthy; Low, Steven; Chertkov, Michael
2015-07-21
The AC power flow equations underlie all operational aspects of power systems. They are solved routinely in operational practice using the Newton-Raphson method and its variants. These methods work well given a good initial “guess” for the solution, which is always available in normal system operations. However, with the increase in levels of intermittent generation, the assumption of a good initial guess always being available is no longer valid. In this paper, we solve this problem using the theory of monotone operators. We show that it is possible to compute (using an offline optimization) a “monotonicity domain” in the space of voltage phasors. Given this domain, there is a simple efficient algorithm that will either find a solution in the domain, or provably certify that no solutions exist in it. We validate the approach on several IEEE test cases and demonstrate that the offline optimization can be performed tractably and the computed “monotonicity domain” includes all practically relevant power flow solutions.
A scalable approach for high throughput branch flow filtration.
Inglis, David W; Herman, Nick
2013-05-07
Microfluidic continuous flow filtration methods have the potential for very high size resolution using minimum feature sizes that are larger than the separation size, thereby circumventing the problem of clogging. Branch flow filtration is particularly promising because it has an unlimited dynamic range (ratio of largest passable particle to the smallest separated particle) but suffers from very poor volume throughput because when many branches are used, they cannot be identical if each is to have the same size cut-off. We describe a new iterative approach to the design of branch filtration devices able to overcome this limitation without large dead volumes. This is demonstrated by numerical modelling, fabrication and testing of devices with 20 branches, with dynamic ranges up to 6.9, and high filtration ratios (14-29%) on beads and fungal spores. The filters have a sharp size cutoff (10× depletion for 12% size difference), with large particle rejection equivalent to a 20th order Butterworth low pass filter. The devices are fully scalable, enabling higher throughput and smaller cutoff sizes and they are compatible with ultra low cost fabrication.
Distribution system power flow analysis; A rigid approach
Chen, T.H.; Chen, M.S.; Hwang, K.J. . Energy Systems Research Center); Kotas, P.; Chebli, E.A. )
1991-07-01
This paper introduces a rigid approach to three-phase distribution power flow analysis for large-scale distribution systems. This approach is oriented toward applications in distribution system operational analysis rather than planning analysis. This difference should be properly emphasized, otherwise, the misuse of the planning-type method to analyze the operational behavior of the system will distort the explanation of the calculated results and lead to incorrect conclusions. The solution method is the optimally ordered triangular factorization Y{sub Bus} Method (implicit Z{sub Bus} Gauss Method) which not only takes advantage of the sparsity of system equations but also has very good convergence characteristics on distribution problems. Detailed component models and suitable solution techniques are the essence of an accurate simulation. Detailed component models, therefore, are needed for all system components in the simulation. Utilizing the phase frame representation for all network elements, a program, entitled Generalized Distribution Analysis Systems - GDAS, with a number of features and capabilities not found in existing packages has been developed for large-scale distribution system simulations. The system being analyzed can be balanced or unbalanced and can be a radial, network, or mixed type distribution system. Furthermore, because the individual phase representation is employed for both system and component models, the system can comprise single, double, and three-phase systems simultaneously. Additionally, with detailed component models, the program can also perform system loss and contingency analyses.
Håkansson, Andreas; Magnusson, Emma; Bergenståhl, Björn; Nilsson, Lars
2012-08-31
Direct determination of hydrodynamic radius from retention time is an advantage of the field-flow fractionation techniques. However, this is not always completely straight forward since non-idealities exist and assumptions have been made in deriving the retention equations. In this study we investigate the effect on accuracy from two factors: (1) level of sophistication of the equations used to determine channel height from a calibration experiment and (2) the influence of secondary relaxation on the accuracy of hydrodynamic radius determination. A new improved technique for estimating the channel height from calibration experiments is suggested. It is concluded that severe systematic error can arise if the most common channel height equations are used and an alternative more rigorous approach is described. For secondary relaxation it is concluded that this effect increases with the cross-flow decay rate. The secondary relaxation effect is quantified for different conditions. This is part one of two. In the second part the determination of hydrodynamic radius are evaluated experimentally under similar conditions.
Flow cytometric and laser scanning microscopic approaches in epigenetics research.
Szekvolgyi, Lorant; Imre, Laszlo; Minh, Doan Xuan Quang; Hegedus, Eva; Bacso, Zsolt; Szabo, Gabor
2009-01-01
Our understanding of epigenetics has been transformed in recent years by the advance of technological possibilities based primarily on a powerful tool, chromatin immunoprecipitation (ChIP). However, in many cases, the detection of epigenetic changes requires methods providing a high-throughput (HTP) platform. Cytometry has opened a novel approach for the quantitative measurement of molecules, including PCR products, anchored to appropriately addressed microbeads (Pataki et al. 2005. Cytometry 68, 45-52). Here we show selected examples for the utility of two different cytometry-based platforms of epigenetic analysis: ChIP-on-beads, a flow-cytometric test of local histone modifications (Szekvolgyi et al. 2006. Cytometry 69, 1086-1091), and the laser scanning cytometry-based measurement of global epigenetic modifications that might help predict clinical behavior in different pathological conditions. We anticipate that such alternative tools may shortly become indispensable in clinical practice, translating the systematic screening of epigenetic tags from basic research into routine diagnostics of HTP demand.
Unsteady flow phenomena in human undulatory swimming: a numerical approach.
Pacholak, Steffen; Hochstein, Stefan; Rudert, Alexander; Brücker, Christoph
2014-06-01
The undulatory underwater sequence is one of the most important phases in competitive swimming. An understanding of the recurrent vortex dynamics around the human body and their generation could therefore be used to improve swimming techniques. In order to produce a dynamic model, we applied human joint kinematics to three-dimensional (3D) body scans of a female swimmer. The flow around this dynamic model was then calculated using computational fluid dynamics with the aid of moving 3D meshes. Evaluation of the numerical results delivered by the various motion cycles identified characteristic vortex structures for each of the cycles, which exhibited increasing intensity and drag influence. At maximum thrust, drag forces appear to be 12 times higher than those of a passive gliding swimmer. As far as we know, this is the first disclosure of vortex rings merging into vortex tubes in the wake after vortex recapturing. All unsteady structures were visualized using a modified Q-criterion also incorporated into our methods. At the very least, our approach is likely to be suited to further studies examining swimmers engaging in undulatory swimming during training or competition.
Flow field design development using the segmented cell approach
Bender, G.; Ramsey, J. C.
2002-01-01
We report on fuel cell flow-field development employing two-dimensional computational fluid dynamics (2-D CFD). Simulation of the flow distribution of a parallel channel flow-field, with a simple one-channel manifold, predicted inhomogeneous performance distribution within the cell. Further modeling, focusing on modification of the inlet and outlet flow fields, was used to predict a more homogeneous flow distribution in the flow-field. Attempts were made to verify the theoretical predictions experimentally by application of the segmented cell system. Measurements of the current distribution and CO transient response supported the 2-D CFD predictions. However, the margin of error between predicted and experimental results was considered insufficient to be of practical use. Future work will involve the evaluation of 3-D CFD to achieve the appropriate level of accuracy.
A Novel Approach to Adaptive Flow Separation Control
2016-09-03
net prediction signal (dotted curve) to adjust to match the measured signal (solid curve) even when the flow conditions change. SBMPC is then...A second series of PIV measurements of the same duration was collected to characterize the controlled flow . Contours of streamwise velocity V_x are...SECURITY CLASSIFICATION OF: Due to their practical import, flow control problems have attracted increasing attention. This research specifically
Novel approaches to analysis by flow injection gradient titration.
Wójtowicz, Marzena; Kozak, Joanna; Kościelniak, Paweł
2007-09-26
Two novel procedures for flow injection gradient titration with the use of a single stock standard solution are proposed. In the multi-point single-line (MP-SL) method the calibration graph is constructed on the basis of a set of standard solutions, which are generated in a standard reservoir and subsequently injected into the titrant. According to the single-point multi-line (SP-ML) procedure the standard solution and a sample are injected into the titrant stream from four loops of different capacities, hence four calibration graphs are able to be constructed and the analytical result is calculated on the basis of a generalized slope of these graphs. Both approaches have been tested on the example of spectrophotometric acid-base titration of hydrochloric and acetic acids with using bromothymol blue and phenolphthalein as indicators, respectively, and sodium hydroxide as a titrant. Under optimized experimental conditions the analytical results of precision less than 1.8 and 2.5% (RSD) and of accuracy less than 3.0 and 5.4% (relative error (RE)) were obtained for MP-SL and SP-ML procedures, respectively, in ranges of 0.0031-0.0631 mol L(-1) for samples of hydrochloric acid and of 0.1680-1.7600 mol L(-1) for samples of acetic acid. The feasibility of both methods was illustrated by applying them to the total acidity determination in vinegar samples with precision lower than 0.5 and 2.9% (RSD) for MP-SL and SP-ML procedures, respectively.
An Active, Collaborative Approach to Learning Skills in Flow Cytometry
ERIC Educational Resources Information Center
Fuller, Kathryn; Linden, Matthew D.; Lee-Pullen, Tracey; Fragall, Clayton; Erber, Wendy N.; Röhrig, Kimberley J.
2016-01-01
Advances in science education research have the potential to improve the way students learn to perform scientific interpretations and understand science concepts. We developed active, collaborative activities to teach skills in manipulating flow cytometry data using FlowJo software. Undergraduate students were given compensated clinical flow…
An Active, Collaborative Approach to Learning Skills in Flow Cytometry
ERIC Educational Resources Information Center
Fuller, Kathryn; Linden, Matthew D.; Lee-Pullen, Tracey; Fragall, Clayton; Erber, Wendy N.; Röhrig, Kimberley J.
2016-01-01
Advances in science education research have the potential to improve the way students learn to perform scientific interpretations and understand science concepts. We developed active, collaborative activities to teach skills in manipulating flow cytometry data using FlowJo software. Undergraduate students were given compensated clinical flow…
Limiting flows of a viscous fluid with stationary separation zones with Re approaching infinity
NASA Technical Reports Server (NTRS)
Taganov, G. I.
1982-01-01
The limiting flows of a viscous noncondensable fluid, which are approached by flows with stationary separation zones behind planar symmetrical bodies, with an unlimited increase in the Reynolds number are studied. Quantitative results are obtained in the case of a circulation flow inside of a separation zone.
A Bayesian approach to flow record infilling and extension for reservoir design
NASA Astrophysics Data System (ADS)
Jones, D. A.; Sene, K. J.
A Bayesian approach is described for dealing with the problem of infilling and generating stochastic flow sequences using rainfall data to guide the flow generation process, and including bounded (censored) observed flow and rainfall data to provide additional information. Solutions are obtained using a Gibbs sampling procedure. Particular problems discussed include developing new procedures for fitting transformations when bounded values are available, coping with additional information in the form of values, or bounds, for totals of flows across several sites, and developing relationships between annual flow and rainfall data. Examples are shown of both infilled values of unknown past river flows, with assessment of uncertainty, and realisations of flows representative of what might occur in the future. Several procedures for validating the model output are described and the central estimates of flows, taken as a surrogate for historical observed flows, are compared with long term regional flow and rainfall data.
A Riparian Approach to Dendrochronological Flow Reconstruction, Yellowstone River, Montana
NASA Astrophysics Data System (ADS)
Schook, D. M.; Rathburn, S. L.; Friedman, J. M.
2015-12-01
Tree ring-based flow reconstructions can reveal river discharge variability over durations far exceeding the gauged record, building perspective for both the measured record and future flows. We use plains cottonwood (Populus deltoides subsp. monilifera) tree rings collected from four rivers to reconstruct flow history of the Yellowstone River near its confluence with the Missouri River. Upland trees in dry regions are typically used in flow reconstruction because their annual growth is controlled by the same precipitation that drives downstream flow, but our study improves flow reconstruction by including floodplain trees that are directly affected by the river. Cores from over 1000 cottonwoods along the Yellowstone, Powder, Little Missouri, and Redwater Rivers were collected from within a 170 km radius to reconstruct flows using the Age Curve Standardization technique in a multiple regression analysis. The large sample from trees spanning many age classes allows us to use only the rings that were produced when each tree was less than 50 years old and growth was most strongly correlated to river discharge. Using trees from a range of rivers improves our ability to differentiate between growth resulting from local precipitation and river flow, and we show that cottonwood growth differs across these neighboring rivers having different watersheds. Using the program Seascorr, tree growth is found to better correlated to seasonal river discharge (R = 0.69) than to local precipitation (R = 0.45). Our flow reconstruction reveals that the most extreme multi-year or multi-decade drought periods of the last 250 years on either the Yellowstone (1817-1821) or Powder (1846-1865) Rivers are missed by the gauged discharge record. Across all sites, we document increased growth in the 20th century compared to the 19th, a finding unattainable with conventional methods but having important implications for flow management.
Three Dimensional Alveolar Flow Phenomena Using a CFD Approach
NASA Astrophysics Data System (ADS)
Sznitman, Josue
2005-11-01
Respiratory flows in the lung periphery are characterized by low Reynolds numbers (typically Re<1) in sub-millimeter airways marked by the presence of alveoli (gas exchange units). We present for realistic breathing conditions using CFD simulations (CFX-5.7.1), 3D velocity fields and flow patterns induced by the expansion/contraction of alveoli and acinar ducts during oscillatory flow. Based on anatomical data, the alveolus and airway are modeled as a spherical cap connected to a cylindrical duct, both subject to moving wall boundary conditions simulating respiration. The resulting 3D flow patterns are complex and governed by the ratio of the alveolar to ductal flow rates. This ratio describes the interplay between alveolar recirculation, induced by the ductal shear flow over the alveolus opening, and alveolar radial flow, induced by the expansion/contraction motion. Our 3D results are in good agreement with 2D simulations reported in the literature. Although convection mechanisms may transport gas along acinar ducts and deeper into the acinus, velocity fields within alveoli predict that upon gas entering them, transport is then solely dominated by diffusion mechanisms.
A Risk-Based Ecohydrological Approach to Assessing Environmental Flow Regimes.
Mcgregor, Glenn B; Marshall, Jonathan C; Lobegeiger, Jaye S; Holloway, Dean; Menke, Norbert; Coysh, Julie
2017-03-27
For several decades there has been recognition that water resource development alters river flow regimes and impacts ecosystem values. Determining strategies to protect or restore flow regimes to achieve ecological outcomes is a focus of water policy and legislation in many parts of the world. However, consideration of existing environmental flow assessment approaches for application in Queensland identified deficiencies precluding their adoption. Firstly, in managing flows and using ecosystem condition as an indicator of effectiveness, many approaches ignore the fact that river ecosystems are subjected to threatening processes other than flow regime alteration. Secondly, many focus on providing flows for responses without considering how often they are necessary to sustain ecological values in the long-term. Finally, few consider requirements at spatial-scales relevant to the desired outcomes, with frequent focus on individual places rather than the regions supporting sustainability. Consequently, we developed a risk-based ecohydrological approach that identifies ecosystem values linked to desired ecological outcomes, is sensitive to flow alteration and uses indicators of broader ecosystem requirements. Monitoring and research is undertaken to quantify flow-dependencies and ecological modelling is used to quantify flow-related ecological responses over an historical flow period. The relative risk from different flow management scenarios can be evaluated at relevant spatial-scales. This overcomes the deficiencies identified above and provides a robust and useful foundation upon which to build the information needed to support water planning decisions. Application of the risk assessment approach is illustrated here by two case studies.
A sensitivity equation approach to shape optimization in fluid flows
NASA Technical Reports Server (NTRS)
Borggaard, Jeff; Burns, John
1994-01-01
A sensitivity equation method to shape optimization problems is applied. An algorithm is developed and tested on a problem of designing optimal forebody simulators for a 2D, inviscid supersonic flow. The algorithm uses a BFGS/Trust Region optimization scheme with sensitivities computed by numerically approximating the linear partial differential equations that determine the flow sensitivities. Numerical examples are presented to illustrate the method.
A novel approach to improve operation and performance in flow field-flow fractionation.
Johann, Christoph; Elsenberg, Stephan; Roesch, Ulrich; Rambaldi, Diana C; Zattoni, Andrea; Reschiglian, Pierluigi
2011-07-08
A new system design and setup are proposed for the combined use of asymmetrical flow field-flow fractionation (AF4) and hollow-fiber flow field-flow fractionation (HF5) within the same instrumentation. To this purpose, three innovations are presented: (a) a new flow control scheme where focusing flow rates are measured in real time allowing to adjust the flow rate ratio as desired; (b) a new HF5 channel design consisting of two sets of ferrule, gasket and cap nut used to mount the fiber inside a tube. This design provides a mechanism for effective and straightforward sealing of the fiber; (c) a new AF4 channel design with only two fluid connections on the upper plate. Only one pump is needed to deliver the necessary flow rates. In the focusing/relaxation step the two parts of the focusing flow and a bypass flow flushing the detectors are created with two splits of the flow from the pump. In the elution mode the cross-flow is measured and controlled with a flow controller device. This leads to reduced pressure pulsations in the channel and improves signal to noise ratio in the detectors. Experimental results of the separation of bovine serum albumin (BSA) and of a mix of four proteins demonstrate a significant improvement in the HF5 separation performance, in terms of efficiency, resolution, and run-to-run reproducibility compared to what has been reported in the literature. Separation performance in HF5 mode is shown to be comparable to the performance in AF4 mode using a channel with two connections in the upper plate.
A comparison of stabilisation approaches for finite-volume simulation of viscoelastic fluid flow
NASA Astrophysics Data System (ADS)
Chen, Xingyuan; Marschall, Holger; Schäfer, Michael; Bothe, Dieter
2013-07-01
In this work we compare different stabilisation approaches currently used in the simulation of viscoelastic fluid flow. These approaches are: the both-sides diffusion, the positive definiteness preserving scheme, the log-conformation tensor representation and the symmetry factorisation of the conformation tensor. The evaluation of these approaches is done regarding their implementation complexity, stability, accuracy, efficiency and applicability to complex problems. Their performances are examined for an Oldroyd-B fluid in the test cases of lid-driven cavity, flow past a cylinder and 4:1 contraction flow. We summarise the situations in which the different approaches can be recommended.
Numerical and Experimental Approaches Toward Understanding Lava Flow Heat Transfer
NASA Astrophysics Data System (ADS)
Rumpf, M.; Fagents, S. A.; Hamilton, C.; Crawford, I. A.
2013-12-01
We have performed numerical modeling and experimental studies to quantify the heat transfer from a lava flow into an underlying particulate substrate. This project was initially motivated by a desire to understand the transfer of heat from a lava flow into the lunar regolith. Ancient regolith deposits that have been protected by a lava flow may contain ancient solar wind, solar flare, and galactic cosmic ray products that can give insight into the history of our solar system, provided the records were not heated and destroyed by the overlying lava flow. In addition, lava-substrate interaction is an important aspect of lava fluid dynamics that requires consideration in lava emplacement models Our numerical model determines the depth to which the heat pulse will penetrate beneath a lava flow into the underlying substrate. Rigorous treatment of the temperature dependence of lava and substrate thermal conductivity and specific heat capacity, density, and latent heat release are imperative to an accurate model. Experiments were conducted to verify the numerical model. Experimental containers with interior dimensions of 20 x 20 x 25 cm were constructed from 1 inch thick calcium silicate sheeting. For initial experiments, boxes were packed with lunar regolith simulant (GSC-1) to a depth of 15 cm with thermocouples embedded at regular intervals. Basalt collected at Kilauea Volcano, HI, was melted in a gas forge and poured directly onto the simulant. Initial lava temperatures ranged from ~1200 to 1300 °C. The system was allowed to cool while internal temperatures were monitored by a thermocouple array and external temperatures were monitored by a Forward Looking Infrared (FLIR) video camera. Numerical simulations of the experiments elucidate the details of lava latent heat release and constrain the temperature-dependence of the thermal conductivity of the particulate substrate. The temperature-dependence of thermal conductivity of particulate material is not well known
Granular surface flow via successive destabilization: A continuum approach
NASA Astrophysics Data System (ADS)
Hoffmann, Andreas; Linz, Stefan J.
2010-11-01
Global and localized granular surface flow is analyzed in a model that takes into account the basic forces between a flowing granular layer and an underlying granular bed. Starting from a quantitatively correct description of global stick-slip avalanches on the surfaces of heaps we are able to describe localized flows of various types as seen in experiments of Daerr and Douady [A. Daerr, S. Douady, Two types of avalanche behavior in granular media, Nature (London) 399 (1999) 241]. The descriptive level takes into account the free surface and the velocity of the flow solely. We limit our model to cases where this surface is effectively one-dimensional so that our model equations are consequently one-dimensional in space. With this kind of description we are able to account for the tight coupling between local grain velocity and local height of the so-called lonely waves. Our model shows the nature of a wave of mobilization and deposition. Granular material is set into motion in a domino-like manner. In addition destabilization of material behind an avalanche is taken into account. The front velocities are found to be constant and in general head and rear front travel with the same velocity in our model. The front velocities depend on the tilt angle of the heap that those localized structures run down on. A critical angle is observed above which the rear front velocity abruptly switches sign from positive (downslope) to negative (upslope) values. Furthermore, we find global influences of the surface shape of a flowing granular layer on Bagnold friction. This characteristic collisional friction between flowing layers and beds is shown to cause S-shaping of the free surface for rapid flow velocities. Finally, our model also explains the power spectrum of avalanches as experimentally detected by Jaeger et al. [H. Jaeger, C. Liu, S. Nagel, Relaxation at the angle of repose, Phys. Rev. Lett. 62 (1989) 40].
Wall Driven Cavity Approach to Slug Flow Modeling In a Micro channel
NASA Astrophysics Data System (ADS)
Sahu, Avinash; Kulkarni, Shekhar; Pushpavanam, Subramaniam; Pushpavanam Research League Team, Prof.
2014-03-01
Slug flow is a commonly observed stable regime and occurs at relatively low flow rates of the fluids. Wettability of channel decides continuous and discrete phases. In these types of biphasic flows, the fluid - fluid interface acts as a barrier that prohibits species movement across the interface. The flow inside a slug is qualitatively similar to the well known shallow cavity flow. In shallow cavities the flow mimics the ``fully developed'' internal circulation in slug flows. Another approach to slug flow modeling can be in a moving reference frame. Here the wall boundary moves in the direction opposite to that of the flow, hence induces circulations within the phases which is analogous to the well known Lid Driven Cavity. The two parallel walls are moved in the opposite directions which generate circulation patterns, equivalent to the ones regularly observed in slug flow in micro channels. A fourth order stream function equation is solved using finite difference approach. The flow field obtained using the two approaches will be used to analyze the effect on mass transfer and chemical reactions in the micro channel. The internal circulations and the performance of these systems will be validated experimentally.
A new approach to highly resolved measurements of turbulent flow
NASA Astrophysics Data System (ADS)
Puczylowski, J.; Hölling, A.; Peinke, J.; Bhiladvala, R.; Hölling, M.
2015-05-01
In this paper we present the design and principle of a new anemometer, namely the 2d-Laser Cantilever Anemometer (2d-LCA), which has been developed for highly resolved flow speed measurements of two components (2d) under laboratory conditions. We will explain the working principle and demonstrate the sensor’s performance by means of comparison measurements of wake turbulence with a commercial X-wire. In the past we have shown that the 2d-LCA is capable of being applied in liquid and particle-laden domains, but we also believe that other challenging areas of operation such as near-wall flows can become accessible.
Laminar flow transition: A large-eddy simulation approach
NASA Technical Reports Server (NTRS)
Biringen, S.
1982-01-01
A vectorized, semi-implicit code was developed for the solution of the time-dependent, three dimensional equations of motion in plane Poiseuille flow by the large-eddy simulation technique. The code is tested by comparing results with those obtained from the solutions of the Orr-Sommerfeld equation. Comparisons indicate that finite-differences employed along the cross-stream direction act as an implicit filter. This removes the necessity of explicit filtering along this direction (where a nonhomogeneous mesh is used) for the simulation of laminar flow transition into turbulence in which small scale turbulence will be accounted for by a subgrid scale turbulence model.
Extended 3D Approach for Quantification of Abnormal Ascending Aortic Flow
Sigovan, Monica; Dyverfeldt, Petter; Wrenn, Jarrett; Tseng, Elaine E.; Saloner, David; Hope, Michael D.
2015-01-01
Background Flow displacement quantifies eccentric flow, a potential risk factor for aneurysms in the ascending aorta, but only at a single anatomic location. The aim of this study is to extend flow displacement analysis to 3D in patients with aortic and aortic valve pathologies. Methods 43 individuals were studied with 4DFlow MRI in 6 groups: healthy, tricuspid aortic valve (TAV) with aortic stenosis (AS) but no dilatation, TAV with dilatation but no AS, and TAV with both AS and dilatation, BAV without AS or dilatation, BAV without AS but with dilation. The protocol was approved by our institutional review board, and informed consent was obtained. Flow displacement was calculated for multiple planes along the ascending aorta, and 2D and 3D analyses were compared. Results Good correlation was found between 2D flow displacement and both maximum and average 3D values (r>0.8). Healthy controls had significantly lower flow displacement values with all approaches (p<0.05). The highest flow displacement was seen with stenotic TAV and aortic dilation (0.24±0.02 with maximum flow displacement). The 2D approach underestimated the maximum flow displacement by more than 20% in 13 out of 36 patients (36%). Conclusions The extended 3D flow displacement analysis offers a more comprehensive quantitative evaluation of abnormal systolic flow in the ascending aorta than 2D analysis. Differences between patient subgroups are better demonstrated, and maximum flow displacement is more reliable assessed. PMID:25721998
Computational Approaches to the Study of Reactive Flow Mixing.
1980-02-13
Rayleigh - Taylor instability during much of the time the energy is being released. A perturbation , whose wavelength is comparable to the... instability grows initially at wavelengths characteristic of the entrance flow. For certain experimental designs the instability may be essentially two...the effects of buoyancy, Taylor instability arising naturally in larger vortices and vortex streets, and Rayleigh - Taylor instability mixing where
A Maximal Flow Approach to Dynamic Routing in Communication Networks,
1980-05-01
of nodes. In Appendix B we provide a computer program in Fortran for finding the maximal flow in these networks, based on the algorithm of Edmons and... Edmons and Karp is implemented by a Fortran Subroutine called MAXFL. The algorithm finds the shortest path between source and destination on which an
A new approach to flow simulation using hybrid models
NASA Astrophysics Data System (ADS)
Solgi, Abazar; Zarei, Heidar; Nourani, Vahid; Bahmani, Ramin
2017-01-01
The necessity of flow prediction in rivers, for proper management of water resource, and the need for determining the inflow to the dam reservoir, designing efficient flood warning systems and so forth, have always led water researchers to think about models with high-speed response and low error. In the recent years, the development of Artificial Neural Networks and Wavelet theory and using the combination of models help researchers to estimate the river flow better and better. In this study, daily and monthly scales were used for simulating the flow of Gamasiyab River, Nahavand, Iran. The first simulation was done using two types of ANN and ANFIS models. Then, using wavelet theory and decomposing input signals of the used parameters, sub-signals were obtained and were fed into the ANN and ANFIS to obtain hybrid models of WANN and WANFIS. In this study, in addition to the parameters of precipitation and flow, parameters of temperature and evaporation were used to analyze their effects on the simulation. The results showed that using wavelet transform improved the performance of the models in both monthly and daily scale. However, it had a better effect on the monthly scale and the WANFIS was the best model.
Design considerations for pulsed-flow comprehensive two-dimensional GC: dynamic flow model approach.
Harvey, Paul McA; Shellie, Robert A; Haddad, Paul R
2010-04-01
A dynamic flow model, which maps carrier gas pressures and carrier gas flow rates through the first dimension separation column, the modulator sample loop, and the second dimension separation column(s) in a pulsed-flow modulation comprehensive two-dimensional gas chromatography (PFM-GCxGC) system is described. The dynamic flow model assists design of a PFM-GCxGC modulator and leads to rapid determination of pneumatic conditions, timing parameters, and the dimensions of the separation columns and connecting tubing used to construct the PFM-GCxGC system. Three significant innovations are introduced in this manuscript, which were all uncovered by using the dynamic flow model. A symmetric flow path modulator improves baseline stability, appropriate selection of the flow restrictors in the first dimension column assembly provides a generally more stable and robust system, and these restrictors increase the modulation period flexibility of the PFM-GCxGC system. The flexibility of a PFM-GCxGC system resulting from these innovations is illustrated using the same modulation interface to analyze Special Antarctic Blend (SAB) diesel using 3 s and 9 s modulation periods.
Rheological flow laws for multiphase magmas: An empirical approach
NASA Astrophysics Data System (ADS)
Pistone, Mattia; Cordonnier, Benoît; Ulmer, Peter; Caricchi, Luca
2016-07-01
The physical properties of magmas play a fundamental role in controlling the eruptive dynamics of volcanoes. Magmas are multiphase mixtures of crystals and gas bubbles suspended in a silicate melt and, to date, no flow laws describe their rheological behaviour. In this study we present a set of equations quantifying the flow of high-viscosity (> 105 Pa·s) silica-rich multiphase magmas, containing both crystals (24-65 vol.%) and gas bubbles (9-12 vol.%). Flow laws were obtained using deformation experiments performed at high temperature (673-1023 K) and pressure (200-250 MPa) over a range of strain-rates (5 · 10- 6 s- 1 to 4 · 10- 3 s- 1), conditions that are relevant for volcanic conduit processes of silica-rich systems ranging from crystal-rich lava domes to crystal-poor obsidian flows. We propose flow laws in which stress exponent, activation energy, and pre-exponential factor depend on a parameter that includes the volume fraction of weak phases (i.e. melt and gas bubbles) present in the magma. The bubble volume fraction has opposing effects depending on the relative crystal volume fraction: at low crystallinity bubble deformation generates gas connectivity and permeability pathways, whereas at high crystallinity bubbles do not connect and act as ;lubricant; objects during strain localisation within shear bands. We show that such difference in the evolution of texture is mainly controlled by the strain-rate (i.e. the local stress within shear bands) at which the experiments are performed, and affect the empirical parameters used for the flow laws. At low crystallinity (< 44 vol.%) we observe an increase of viscosity with increasing strain-rate, while at high crystallinity (> 44 vol.%) the viscosity decreases with increasing strain-rate. Because these behaviours are also associated with modifications of sample textures during the experiment and, thus, are not purely the result of different deformation rates, we refer to ;apparent shear-thickening; and
Study of rarefaction effects in gas flows with particle approaches
NASA Astrophysics Data System (ADS)
Ngalande, Cedrick Goliati
The objective of this study is the numerical analysis of gas flow rarefaction phenomena with application to a number of aerospace-related problems. The understanding and accurate numerical prediction of rarefied flow regime is important both for aerospace systems that operate in this regime, and for the development of new generation of gasdriven nano- and micro-scale devices, for which the gas mean free path is comparable with the reference flow scale and rarefaction effects are essential. The main tool for the present analysis is the direct simulations Monte Carlo (DSMC) method. The first topic is the study of rarefied flows in the CHAFF-IV facility. A test particle method was used to analyse the pumping efficiency of CHAFF-IV, and determine optimum geometrical configuration of the chamber. The second topic under consideration is the influence of the surface roughness on nozzle plume flow and plume impingement for different flow regimes from free molecular to near-continuum. Surface roughness effects in rocket nozzles are found to be significant only in very rarefied flows where Reynolds number is about unity. The third topic is the effect of rarefaction on radiometric forces. This effect is shown to be an important factor affecting the radiometric forces. The maximum radiometric forces for all gases under consideration are observed at a Knudsen number of about 0.1. For a radiometer vane placed in a finite size chamber, the maximum force was found to be roughly proportional to the surface area of the vane. This is an indication that the collision-less area force, and not thermal transpiration edge force, dominates the radiometric phenomena in that regime. The role of molecular diameter, viscosity and chamber size on radiometric forces have been found to be significant. The forth topic is the numerical study of the interaction between optical lattices created by two counter-propagating laser beams and initially stagnant gases, in the entire flow regime from free
NASA Astrophysics Data System (ADS)
Shafii, Mahyar; Basu, Nandita; Craig, James R.; Schiff, Sherry L.; Van Cappellen, Philippe
2017-04-01
Hydrologic models are often tasked with replicating historical hydrographs but may do so without accurately reproducing the internal hydrological functioning of the watershed, including the flow partitioning, which is critical for predicting solute movement through the catchment. Here we propose a novel partitioning-focused calibration technique that utilizes flow-partitioning coefficients developed based on the pioneering work of L'vovich (1979). Our hypothesis is that inclusion of the L'vovich partitioning relations in calibration increases model consistency and parameter identifiability and leads to superior model performance with respect to flow partitioning than using traditional hydrological signatures (e.g., flow duration curve indices) alone. The L'vovich approach partitions the annual precipitation into four components (quick flow, soil wetting, slow flow, and evapotranspiration) and has been shown to work across a range of climatic and landscape settings. A new diagnostic multicriteria model calibration methodology is proposed that first quantifies four calibration measures for watershed functions based on the L'vovich theory, and then utilizes them as calibration criteria. The proposed approach is compared with a traditional hydrologic signature-based calibration for two conceptual bucket models. Results reveal that the proposed approach not only improves flow partitioning in the model compared to signature-based calibration but is also capable of diagnosing flow-partitioning inaccuracy and suggesting relevant model improvements. Furthermore, the proposed partitioning-based calibration approach is shown to increase parameter identifiability. This model calibration approach can be readily applied to other models.
NASA Astrophysics Data System (ADS)
Zhang, Yongbin
2015-06-01
Quantitative comparisons were made between the flow factor approach model and the molecular dynamics simulation (MDS) results both of which describe the flow of a molecularly thin fluid film confined between two solid walls. Although these two approaches, respectively, calculate the flow of a confined molecularly thin fluid film by different ways, very good agreements were found between them when the Couette and Poiseuille flows, respectively, calculated from them were compared. It strongly indicates the validity of the flow factor approach model in modeling the flow of a confined molecularly thin fluid film.
A Cartesian grid approach with hierarchical refinement for compressible flows
NASA Technical Reports Server (NTRS)
Quirk, James J.
1994-01-01
Many numerical studies of flows that involve complex geometries are limited by the difficulties in generating suitable grids. We present a Cartesian boundary scheme for two-dimensional, compressible flows that is unfettered by the need to generate a computational grid and so it may be used, routinely, even for the most awkward of geometries. In essence, an arbitrary-shaped body is allowed to blank out some region of a background Cartesian mesh and the resultant cut-cells are singled out for special treatment. This is done within a finite-volume framework and so, in principle, any explicit flux-based integration scheme can take advantage of this method for enforcing solid boundary conditions. For best effect, the present Cartesian boundary scheme has been combined with a sophisticated, local mesh refinement scheme, and a number of examples are shown in order to demonstrate the efficacy of the combined algorithm for simulations of shock interaction phenomena.
Hydrodynamical Approach to Vehicular Flow in the Urban Street Canyon
NASA Astrophysics Data System (ADS)
Duras, Maciej M.
2001-06-01
The vehicular flow in the urban street canyon is considered. The classical field description is used in the modelling of the vehicular movement and of gaseous mixture in generic urban street canyon. The dynamical variables include vehicular densities, velocities, and emissivities: of pollutants, heat and exhaust gases, as well as standard mixture components' variables: densities, velocities, temperature, pressures. The local balances' equations predict the dynamics of the complex system. The automatic control of the vehicular flow is attained by the sets of coordinated traffic lights. The automatic control is aimed at minimization of traffic ecological costs by the application of variational calculus (Lagrange's and Bolz's problems). The theoretical description is accompanied by numerical examples of computer fluid dynamics based on real traffic data.
A power law approach to orifice flow rate calibration.
Rhinehart, R Russell; Gebreyohannes, Solomon; Sridhar, Upasana Manimegalai; Patrachari, Anirudh; Rahaman, M S
2011-04-01
Although standards for orifice flow meter design, installation, and calibration are supported herein, noncompliant devices exist in many pilot-, lab-scale, and on-board applications. For these, a common calibration practice is to preserve the ideal square root relation and determine a device specific discharge coefficient value. This work provides theoretical and empirical analyses to support relaxing the square root relation between orifice pressure drop and flow rate for noncompliant devices. The resulting power law relation is shown to improve accuracy, precision, and rangeability. Whether a device specific square root or power law model is used, it requires off-line or in-line calibration data. As such, a power law calibration model may only be useful for on-board and small-scale applications.
Joint conditional simulations and the spectral approach for flow modeling
NASA Astrophysics Data System (ADS)
Gutjahr, A.; Bullard, B.; Hatch, S.; Hughson, L.
1994-03-01
The use of data to condition single random fields has a well-established history. However, the joint use of data from several cross-correlated random fields is not as well developed. For example, the use of both transmissivity and head data in a steady state 2-d stochastic flow problem is essentially an inverse problem that is very important for both flow and transport predictions. This problem is addressed here by using a combination of numerical simulation and analytical methods and its application illustrated. The type of information conveyed by the different data categories is explored. The results presented are especially interesting in that head and transmissivity each give different information: Head values would appear to constrain the geometry of the paths while transmissivity data yields information about travel times. The linearized model is expanded to an iterative procedure and the “true” conditional distribution at several locations is compared with the iterative solution. The problem mentioned above is one with a special transfer function specified by the flow equation. In the second part of the paper a Fast Fourier Transform method for generation and conditioning of two or more random fields is introduced. This procedure is simple to implement, fast and very flexible.
Josephson flux-flow oscillator: The microscopic tunneling approach
NASA Astrophysics Data System (ADS)
Gulevich, D. R.; Koshelets, V. P.; Kusmartsev, F. V.
2017-07-01
We elaborate a theoretical description of large Josephson junctions which is based on Werthamer's microscopic tunneling theory. The model naturally incorporates coupling of electromagnetic radiation to the tunnel currents and, therefore, is particularly suitable for description of the self-coupling effect in Josephson junction. In our numerical calculations we treat the arising integro-differential equation, which describes temporal evolution of the superconducting phase difference coupled to the electromagnetic field, by the Odintsov-Semenov-Zorin algorithm. This allows us to avoid evaluation of the time integrals at each time step while taking into account all the memory effects. To validate the obtained microscopic model of large Josephson junction we focus our attention on the Josephson flux-flow oscillator. The proposed microscopic model of flux-flow oscillator does not involve the phenomenological damping parameter, rather the damping is taken into account naturally in the tunnel current amplitudes calculated at a given temperature. The theoretically calculated current-voltage characteristics is compared to our experimental results obtained for a set of fabricated flux-flow oscillators of different lengths.
Field theoretical approach for bio-membrane coupled with flow field
NASA Astrophysics Data System (ADS)
Oya, Y.; Kawakatsu, T.
2013-02-01
Shape deformation of bio-membranes in flow field is well known phenomenon in biological systems, for example red blood cell in blood vessel. To simulate such deformation with use of field theoretical approach, we derived the dynamical equation of phase field for shape of membrane and coupled the equation with Navier-Stokes equation for flow field. In 2-dimensional simulations, we found that a bio-membrane in a Poiseuille flow takes a parachute shape similar to the red blood cells.
Regional Input-Output Tables and Trade Flows: an Integrated and Interregional Non-survey Approach
Boero, Riccardo; Edwards, Brian Keith; Rivera, Michael Kelly
2017-03-20
Regional input–output tables and trade flows: an integrated and interregional non-survey approach. Regional Studies. Regional analyses require detailed and accurate information about dynamics happening within and between regional economies. However, regional input–output tables and trade flows are rarely observed and they must be estimated using up-to-date information. Common estimation approaches vary widely but consider tables and flows independently. Here, by using commonly used economic assumptions and available economic information, this paper presents a method that integrates the estimation of regional input–output tables and trade flows across regions. Examples of the method implementation are presented and compared with other approaches, suggestingmore » that the integrated approach provides advantages in terms of estimation accuracy and analytical capabilities.« less
Wang, W.; Rutqvist, J.; Gorke, U.-J.; Birkholzer, J.T.; Kolditz, O.
2010-03-15
The present work compares the performance of two alternative flow models for the simulation of thermal-hydraulic coupled processes in low permeable porous media: non-isothermal Richards and two-phase flow concepts. Both models take vaporization processes into account: however, the Richards model neglects dynamic pressure variations and bulk flow of the gaseous phase. For the comparison of the two approaches first published data from a laboratory experiment is studied involving thermally driven moisture flow in a partially saturated bentonite sample. Then a benchmark test of longer-term thermal-hydraulic behavior in the engineered barrier system of a geological nuclear waste repository is analyzed (DECOVALEX project). It was found that both models can be used to reproduce the vaporization process if the intrinsic permeability is relative high. However, when a thermal-hydraulic coupled problem has the same low intrinsic permeability for both the liquid and the gas phase, only the two-phase flow approach provides reasonable results.
An Investigation of Power Flow Characteristics of L-Shaped Plates Adopting a Substructure Approach
NASA Astrophysics Data System (ADS)
WANG, Z. H.; XING, J. T.; PRICE, W. G.
2002-02-01
A substructure approach with free-free interface condition is formulated to investigate the power flow characteristics of an L-shaped plate. This is achieved by complementing the normal dynamic equations with geometric compatibility equations allowing the assessment of power flow dynamic characteristics applied to and excited within the system. The displacement contribution of the external and boundary coupling forces is deduced, permitting determination of the power flow between the interfaces of substructures. A power flow density vector is defined and the corresponding power flow lines illustrate the flow of power in the plate. Numerical examples demonstrate the applicability of the method and detailed configurations display the power flow characteristics associated with L-shaped plates. The proposed method can calculate the higher modes easily and efficiently to ensure convergence of solution as well as readily taking into account variations in substructure damping.
Data-driven approach to design of passive flow control strategies
NASA Astrophysics Data System (ADS)
Gómez, F.; Blackburn, H. M.
2017-02-01
An approach to designing passive devices for control of unsteady flows is presented. The method requires only snapshots of the flow to be controlled as inputs. A temporal correlation based on proper orthogonal decomposition of both fluctuating velocity and nonlinear forcing serves to identify the spatial locations in which the forcing drives the different unsteady flow features. The installation of a passive device in these spatial locations inhibits the fluctuating motion. The potential of the methodology is demonstrated via the suppression of vortex shedding in flow past a square cylinder, paving the way to the control of more complex flows using passive devices. Connections in agreement with previous studies targeting the same flow using different passive flow control strategies are provided.
Soares, Joao S.; Gao, Chao; Alemu, Yared; Slepian, Marvin; Bluestein, Danny
2013-01-01
Stresses on blood cellular constituents induced by blood flow can be represented by a continuum approach down to the μm level; however, the molecular mechanisms of thrombosis and platelet activation and aggregation are on the order of nm. The coupling of the disparate length and time scales between molecular and macroscopic transport phenomena represent a major computational challenge. In order to bridge the gap between macroscopic flow scales and the cellular scales with the goal of depicting and predicting flow induced thrombogenicity, multi-scale approaches based on particle methods are better suited. We present a top-scale model to describe bulk flow of platelet suspensions: we employ dissipative particle dynamics to model viscous flow dynamics and present a novel and general no-slip boundary condition that allows the description of three-dimensional viscous flows through complex geometries. Dissipative phenomena associated with boundary layers and recirculation zones are observed and favorably compared to benchmark viscous flow solutions (Poiseuille and Couette flows). Platelets in suspension, modeled as coarse-grained finite-sized ensembles of bound particles constituting an enclosed deformable membrane with flat ellipsoid shape, show self-orbiting motions in shear flows consistent with Jeffery's orbits, and are transported with the flow, flipping and colliding with the walls and interacting with other platelets. PMID:23695489
Soares, Joao S; Gao, Chao; Alemu, Yared; Slepian, Marvin; Bluestein, Danny
2013-11-01
Stresses on blood cellular constituents induced by blood flow can be represented by a continuum approach down to the μm level; however, the molecular mechanisms of thrombosis and platelet activation and aggregation are on the order of nm. The coupling of the disparate length and time scales between molecular and macroscopic transport phenomena represents a major computational challenge. In order to bridge the gap between macroscopic flow scales and the cellular scales with the goal of depicting and predicting flow induced thrombogenicity, multi-scale approaches based on particle methods are better suited. We present a top-scale model to describe bulk flow of platelet suspensions: we employ dissipative particle dynamics to model viscous flow dynamics and present a novel and general no-slip boundary condition that allows the description of three-dimensional viscous flows through complex geometries. Dissipative phenomena associated with boundary layers and recirculation zones are observed and favorably compared to benchmark viscous flow solutions (Poiseuille and Couette flows). Platelets in suspension, modeled as coarse-grained finite-sized ensembles of bound particles constituting an enclosed deformable membrane with flat ellipsoid shape, show self-orbiting motions in shear flows consistent with Jeffery's orbits, and are transported with the flow, flipping and colliding with the walls and interacting with other platelets.
Larry J. Schmidt; John P. Potyondy
2004-01-01
This paper discusses one approach for quantifying channel maintenance instream flow necessary to achieve the Forest Service Organic Act purpose of securing favorable conditions of water flows. The approach is appropriate for quantifying channel maintenance flows on perennial, unregulated, snowmelt-dominated, gravel-bed streams with alluvial reaches. The approach...
Flow Solution for Advanced Separate Flow Nozzles Response A: Structured Grid Navier-Stokes Approach
NASA Technical Reports Server (NTRS)
Kenzakowski, D. C.; Shipman, J.; Dash, S. M.; Saiyed, Naseem (Technical Monitor)
2001-01-01
NASA Glenn Research Center funded a computational study to investigate the effect of chevrons and tabs on the exhaust plume from separate flow nozzles. Numerical studies were conducted at typical takeoff power with 0.28 M flight speed. Report provides numerical data and insights into the mechanisms responsible for increased mixing.
NASA Astrophysics Data System (ADS)
Stancanelli, Laura Maria; Peres, David Johnny; Cancelliere, Antonino; Foti, Enrico
2017-07-01
Rainfall-induced shallow slides can evolve into debris flows that move rapidly downstream with devastating consequences. Mapping the susceptibility to debris flow is an important aid for risk mitigation. We propose a novel practical approach to derive debris flow inundation maps useful for susceptibility assessment, that is based on the integrated use of DEM-based spatially-distributed hydrological and slope stability models with debris flow propagation models. More specifically, the TRIGRS infiltration and infinite slope stability model and the FLO-2D model for the simulation of the related debris flow propagation and deposition are combined. An empirical instability-to-debris flow triggering threshold calibrated on the basis of observed events, is applied to link the two models and to accomplish the task of determining the amount of unstable mass that develops as a debris flow. Calibration of the proposed methodology is carried out based on real data of the debris flow event occurred on 1 October 2009, in the Peloritani mountains area (Italy). Model performance, assessed by receiver-operating-characteristics (ROC) indexes, evidences fairly good reproduction of the observed event. Comparison with the performance of the traditional debris flow modeling procedure, in which sediment and water hydrographs are inputed as lumped at selected points on top of the streams, is also performed, in order to assess quantitatively the limitations of such commonly applied approach. Results show that the proposed method, besides of being more process-consistent than the traditional hydrograph-based approach, can potentially provide a more accurate simulation of debris-flow phenomena, in terms of spatial patterns of erosion and deposition as well on the quantification of mobilized volumes and depths, avoiding overestimation of debris flow triggering volume and, thus, of maximum inundation flow depths.
A kinetic-theory approach to turbulent chemically reacting flows
NASA Technical Reports Server (NTRS)
Chung, P. M.
1976-01-01
The paper examines the mathematical and physical foundations for the kinetic theory of reactive turbulent flows, discussing the differences and relation between the kinetic and averaged equations, and comparing some solutions of the kinetic equations obtained by the Green's function method with those obtained by the approximate bimodal method. The kinetic method described consists essentially in constructing the probability density functions of the chemical species on the basis of solutions of the Langevin stochastic equation for the influence of eddies on the behavior of fluid elements. When the kinetic equations are solved for the structure of the diffusion flame established in a shear layer by the bimodal method, discontinuities in gradients of the mean concentrations at the two flame edges appear. This is a consequence of the bimodal approximation of all distribution functions by two dissimilar half-Maxwellian functions, which is a very crude approximation. These discontinuities do not appear when the solutions are constructed by the Green's function method described here.
Visual guidance based on optic flow: a biorobotic approach.
Franceschini, Nicolas
2004-01-01
This paper addresses some basic questions as to how vision links up with action and serves to guide locomotion in both biological and artificial creatures. The thorough knowledge gained during the past five decades on insects' sensory-motor abilities and the neuronal substrates involved has provided us with a rich source of inspiration for designing tomorrow's self-guided vehicles and micro-vehicles, which will be able to cope with unforeseen events on the ground, under water, in the air, in space, on other planets, and inside the human body. Insects can teach us some useful tricks for designing agile autonomous robots. Since constructing a "biorobot" first requires exactly formulating the biological principles presumably involved, it gives us a unique opportunity of checking the soundness and robustness of these principles by bringing them face to face with the real physical world. "Biorobotics" therefore goes one step beyond computer simulation. It leads to experimenting with real physical robots which have to pass the stringent test of the real world. Biorobotics provide us with a new tool, which can help neurobiologists and neuroethologists to identify and investigate worthwhile issues in the field of sensory-motor control. Here we describe some of the visually guided terrestrial and aerial robots we have developed since 1985 on the basis of our biological findings. All these robots behave in response to the optic flow, i.e., they work by measuring the slip speed of the retinal image. Optic flow is sensed on-board by miniature electro-optical velocity sensors. The very principle of these sensors was based on studies in which we recorded the responses of single identified neurons to single photoreceptor stimulation in a model visual system: the fly's compound eye.
An optical flow approach to tracking colonoscopy video.
Liu, Jianfei; Subramanian, Kalpathi R; Yoo, Terry S
2013-04-01
We can supplement the clinical value of an optical colonoscopy procedure if we can continuously co-align corresponding virtual colonoscopy (from preoperative X-ray CT exam) and optical colonoscopy images. In this work, we demonstrate a computer vision algorithm based on optical flow to compute egomotion from live colonoscopy video, which is then used to navigate and visualize the corresponding patient anatomy from X-ray CT data. The key feature of the algorithm lies in the effective combination of sparse and dense optical flow fields to compute the focus of expansion (FOE); FOE permits independent computation of camera translational and rotational parameters, directly contributing to the algorithm's accuracy and robustness. We performed extensive evaluation via a colon phantom and clinical colonoscopy data. We constructed two colon like phantoms, a straight phantom and a curved phantom to measure actual colonoscopy motion; tracking accuracy was quantitatively evaluated by comparing estimated motion parameters (velocity and displacement) to ground truth. Thirty straight and curved phantom sequences were collected at 10, 15 and 20 mm/s (5 trials at each speed), to simulate typical velocities during colonoscopy procedures. The average error in velocity estimation was within 3 mm/s in both straight and curved phantoms. Displacement error was under 7 mm over a total distance of 287-288 mm in the straight and curved phantoms. Algorithm robustness was successfully demonstrated on 27 optical colonoscopy image sequences from 20 different patients, and spanning 5 different colon segments. Specific sequences among these were chosen to illustrate the algorithm's decreased sensitivity to (1) recording interruptions, (2) errors in colon segmentation, (3) illumination artifacts, (4) presence of fluid, and (5) changes in colon structure, such as deformation, polyp removal, and surgical tool movement during a procedure. Copyright © 2013 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Panday, S.; Huyakorn, P. S.
2004-12-01
Physically-based, spatially-distributed (PBSD) modeling of integrated surface water and groundwater flow is necessary for evaluating the complex processes of runoff, recharge, evapotranspiration, subsurface flow, and baseflow, to comprehensively manage water resources for diverse and competing needs such as conjunctive use, aquifer storage and recovery, flood protection, wetland restoration and minimum flow evaluation. Some current approaches to PBSD modeling of integrated surface and subsurface flow will be discussed. Challenges to PBSD integrated modeling will be presented, and application case studies will be presented.
Spatial dynamics of ecosystem service flows: a comprehensive approach to quantifying actual services
Bagstad, Kenneth J.; Johnson, Gary W.; Voigt, Brian; Villa, Ferdinando
2013-01-01
Recent ecosystem services research has highlighted the importance of spatial connectivity between ecosystems and their beneficiaries. Despite this need, a systematic approach to ecosystem service flow quantification has not yet emerged. In this article, we present such an approach, which we formalize as a class of agent-based models termed “Service Path Attribution Networks” (SPANs). These models, developed as part of the Artificial Intelligence for Ecosystem Services (ARIES) project, expand on ecosystem services classification terminology introduced by other authors. Conceptual elements needed to support flow modeling include a service's rivalness, its flow routing type (e.g., through hydrologic or transportation networks, lines of sight, or other approaches), and whether the benefit is supplied by an ecosystem's provision of a beneficial flow to people or by absorption of a detrimental flow before it reaches them. We describe our implementation of the SPAN framework for five ecosystem services and discuss how to generalize the approach to additional services. SPAN model outputs include maps of ecosystem service provision, use, depletion, and flows under theoretical, possible, actual, inaccessible, and blocked conditions. We highlight how these different ecosystem service flow maps could be used to support various types of decision making for conservation and resource management planning.
Yamamoto, Takehiro; Ueda, Shuya
2013-01-01
Biofilm is a slime-like complex aggregate of microorganisms and their products, extracellular polymer substances, that grows on a solid surface. The growth phenomenon of biofilm is relevant to the corrosion and clogging of water pipes, the chemical processes in a bioreactor, and bioremediation. In these phenomena, the behavior of the biofilm under flow has an important role. Therefore, controlling the biofilm behavior in each process is important. To provide a computational tool for analyzing biofilm growth, the present study proposes a computational model for the simulation of biofilm growth in flows. This model accounts for the growth, decay, detachment and adhesion of biofilms. The proposed model couples the computation of the surrounding fluid flow, using the finite volume method, with the simulation of biofilm growth, using the cellular automaton approach, a relatively low-computational-cost method. Furthermore, a stochastic approach for considering the adhesion process is proposed. Numerical simulations for the biofilm growth on a planar wall and that in an L-shaped rectangular channel were carried out. A variety of biofilm structures were observed depending on the strength of the flow. Moreover, the importance of the detachment and adhesion processes was confirmed.
Adsorbed polymers under flow. A stochastic dynamical system approach
NASA Astrophysics Data System (ADS)
Armstrong, Robert; Jhon, Myung S.
1985-09-01
Recent experiments have shown that porous filters preadsorbed with polymer molecules exhibit an anomalously high pressure drop at high rates of flow. We have modeled the adsorbed polymers as dynamical systems and have found that the introduction of hydrodynamic interaction between molecules destabilizes at a high applied shear. As a direct result this instability will cause the molecules to unravel and stretch far into the cross section of the pore, and thus by inference, cause the observed anomalously high pressure drop. Although much of this paper is devoted to the stability characteristics of the deterministic system, Brownian motion is also considered, and an account of the statistics of the Brownian system when the deterministic system becomes unstable is given. The examples revealed in this paper are not of sufficient complexity to calculate with any accuracy the magnitude of this anomalous pressure drop. We simply present a procedure by which a large variety of more complex models could be undertaken and their ultimate effect clearly understood.
A SPATIOTEMPORAL APPROACH FOR HIGH RESOLUTION TRAFFIC FLOW IMPUTATION
Han, Lee; Chin, Shih-Miao; Hwang, Ho-Ling
2016-01-01
Along with the rapid development of Intelligent Transportation Systems (ITS), traffic data collection technologies have been evolving dramatically. The emergence of innovative data collection technologies such as Remote Traffic Microwave Sensor (RTMS), Bluetooth sensor, GPS-based Floating Car method, automated license plate recognition (ALPR) (1), etc., creates an explosion of traffic data, which brings transportation engineering into the new era of Big Data. However, despite the advance of technologies, the missing data issue is still inevitable and has posed great challenges for research such as traffic forecasting, real-time incident detection and management, dynamic route guidance, and massive evacuation optimization, because the degree of success of these endeavors depends on the timely availability of relatively complete and reasonably accurate traffic data. A thorough literature review suggests most current imputation models, if not all, focus largely on the temporal nature of the traffic data and fail to consider the fact that traffic stream characteristics at a certain location are closely related to those at neighboring locations and utilize these correlations for data imputation. To this end, this paper presents a Kriging based spatiotemporal data imputation approach that is able to fully utilize the spatiotemporal information underlying in traffic data. Imputation performance of the proposed approach was tested using simulated scenarios and achieved stable imputation accuracy. Moreover, the proposed Kriging imputation model is more flexible compared to current models.
Stanisavljevic, Nemanja; Brunner, Paul H
2014-08-01
The novelty of this paper is the demonstration of the effectiveness of combining material flow analysis (MFA) with substance flow analysis (SFA) for decision making in waste management. Both MFA and SFA are based on the mass balance principle. While MFA alone has been applied often for analysing material flows quantitatively and hence to determine the capacities of waste treatment processes, SFA is more demanding but instrumental in evaluating the performance of a waste management system regarding the goals "resource conservation" and "environmental protection". SFA focuses on the transformations of wastes during waste treatment: valuable as well as hazardous substances and their transformations are followed through the entire waste management system. A substance-based approach is required because the economic and environmental properties of the products of waste management - recycling goods, residues and emissions - are primarily determined by the content of specific precious or harmful substances. To support the case that MFA and SFA should be combined, a case study of waste management scenarios is presented. For three scenarios, total material flows are quantified by MFA, and the mass flows of six indicator substances (C, N, Cl, Cd, Pb, Hg) are determined by SFA. The combined results are compared to the status quo in view of fulfilling the goals of waste management. They clearly point out specific differences between the chosen scenarios, demonstrating potentials for improvement and the value of the combination of MFA/SFA for decision making in waste management.
Wilsonian RG-flow approach to holographic transport with momentum dissipation
NASA Astrophysics Data System (ADS)
Tian, Yu; Ge, Xian-Hui; Wu, Shao-Feng
2017-08-01
We systematically present a new approach for studying the coupled linear transport of holographic systems. In this approach, the set of equations for the linear perturbations can be reduced to a first-order nonlinear ordinary differential equation expressed as the radial (renormalization group) flow equation of the transport matrices. As an important application, we use this approach to compute the dc and ac conductivities of a holographic model with momentum dissipation, which can be easily read off from the nonlinear flow equations. This method also works for transport in the presence of an external magnetic field.
How fruit developmental biology makes use of flow cytometry approaches.
Pirrello, Julien; Bourdon, Matthieu; Cheniclet, Catherine; Bourge, Mickaël; Brown, Spencer C; Renaudin, Jean-Pierre; Frangne, Nathalie; Chevalier, Christian
2014-02-01
Fleshy fruit species such as tomato are important because of their nutritional and economic value. Several stages of fruit development such as ovary formation, fruit set, and fruit maturation have already been the subject of many developmental studies. However, fruit growth per se has been much less addressed. Fruit growth like all plant organs depends upon the developmental processes of cell division and cell expansion. The activity of cell divisions sets the number of cells that will compose the fruit; the cell expansion activity then determines its final size. Among the various mechanisms that may influence the determination of cell size, endopolyploidy by the means of endoreduplication, i.e. genome amplification in the absence of mitosis, appears to be of great importance in fleshy fruits. In tomato fruit, endoreduplication is associated with DNA-dependent cell expansion: cell size can reach spectacular levels such as hundreds of times its initial size (e.g. >0.5 mm in diameter), with as much as a 256-fold increase in nuclear DNA content. Using tomato fruit development as a model, recent investigations combining the use of flow cytometry, cellular imaging and molecular analyses have provided new data in favor of the long-standing karyoplasmic ratio theory, stating that cells tend to adjust their cytoplasmic volume to the nuclear DNA content. By establishing a highly structured cellular system where multiple physiological functions are integrated, endoreduplication acts as a morphogenetic factor supporting cell growth during tomato fruit development. In the context of plant breeding, deciphering the mechanisms controlling fruit growth, in particular those connecting the process of nuclear endoreduplication with modulation of gene expression, the regulation of cell size and final fruit size and composition, is necessary to understand better the establishment of fleshy fruit quality traits. © 2013 International Society for Advancement of Cytometry.
NASA Astrophysics Data System (ADS)
Ayvaz, M. Tamer; Gurarslan, Gurhan
2017-10-01
In this study, a new partitioning approach is proposed for nonlinear Muskingum flood routing models with lateral flow contribution. The proposed approach is used to partition the inflow hydrograph into different sub-regions so that each sub-region can have its own model parameters. The main advantage of the proposed approach is its independence from any kind of user intervention during generation of the sub-regions. This is a general and systematic solution approach and may be applied to all of the flood routing applications based on the Muskingum model. Applicability of the proposed approach is evaluated by solving four flood routing applications by considering lateral flow contribution. Identified results indicated that the proposed approach can be effectively used to improve the model identification performance more than 80% in the Muskingum flood routing models.
NASA Astrophysics Data System (ADS)
Stancanelli, L. M.; Foti, E.
2015-04-01
A detailed comparison between the performances of two different approaches to debris flow modelling was carried out. In particular, the results of a mono-phase Bingham model (FLO-2D) and that of a two-phase model (TRENT-2D) obtained from a blind test were compared. As a benchmark test the catastrophic event of 1 October 2009 which struck Sicily causing several fatalities and damage was chosen. The predicted temporal evolution of several parameters of the debris flow (such as flow depth and propagation velocity) was analysed in order to investigate the advantages and disadvantages of the two models in reproducing the global dynamics of the event. An analysis between the models' results with survey data have been carried out, not only for the determination of statistical indicators of prediction accuracy, but also for the application of the Receiver Operator Characteristic (ROC) approach. Provided that the proper rheological parameters and boundary conditions are assigned, both models seem capable of reproducing the inundation areas in a reasonably accurate way. However, the main differences in the application rely on the choice of such rheological parameters. Indeed, within the more user-friendly FLO-2D model the tuning of the parameters must be done empirically, with no evidence of the physics of the phenomena. On the other hand, for the TRENT-2D the parameters are physically based and can be estimated from the properties of the solid material, thus reproducing more reliable results. A second important difference between the two models is that in the first method the debris flow is treated as a homogeneous flow, in which the total mass is kept constant from its initiation in the upper part of the basin to the deposition in a debris fan. In contrast, the second approach is suited to reproduce the erosion and deposition processes and the displaced mass can be directly related to the rainfall event. Application of both models in a highly urbanized area reveals the
NASA Astrophysics Data System (ADS)
Stancanelli, L. M.; Foti, E.
2014-11-01
A detailed comparison between the performances of two different approaches to debris flow modelling has been carried out. In particular, the results of a mono-phase Bingham model (FLO-2D) and these of a two phase model (TRENT-2D) obtained from a blind test have been compared. As a benchmark test the catastrophic event of 1 October 2009 which struck Sicily causing several fatalities and damages has been chosen. The predicted temporal evolution of several parameters of the debris flow (as the flow depths and the propagation velocities) has been analyzed in order to investigate the advantages and disadvantages of the two models in reproducing the global dynamics of the event. Analysis between the models results with survey data have been carried out, not only for the determination of statistical indicators of prediction accuracy, but also for the application of the Receiver Operator Characteristic (ROC) approach. Provided that the proper rheological parameters and boundary conditions are assigned, both models seem capable of reproducing the inundation areas in a fairly good way. However, the main differences in the application rely in the choice of such rheological parameters. Indeed, within the more user friendly FLO-2D model the tuning of the parameters must be done empirically, with no evidence of the physics of the phenomena. On the other hand, for the TRENT-2D the parameters are physically based and can be estimated from the properties of the solid material, thus reproducing more reliable results. A second important difference between the two models is that in the first method the debris flow is treated as homogeneous flow, in which the total mass is kept constant from initiation in the upper part of the basin up to the deposition on debris fan. On the contrary, the second approach is suite to reproduce the erosion and deposition processes and the displaced mass can be directly related to the rainfall event. Application of both models in an highly urbanized area
NASA Astrophysics Data System (ADS)
Shiau, Jenq-Tzong; Wu, Fu-Chun
2010-08-01
Environmental flow schemes may be implemented through active or restrictive strategies. The former may be applied via reservoir releases, and the latter can be executed by reducing water demands. We present a dual active-restrictive approach to devising the optimal reservoir operation rules that aim to secure off-stream water supplies while maximizing environmental benefits. For the active part, a multicomponent environmental flow target (including the minimum and monthly flows) is incorporated in the operation rules. For the restrictive counterpart, we use a novel demands partitioning and prioritizing (DPP) approach to reallocating the demands of various sectors. The DPP approach partitions the existing off-stream demand and newly incorporated environmental demand and reassembles the two as the first- and second-priority demands. Water is reallocated to each demand according to the ratios derived from the prioritized demands. The proposed approach is coupled with a multicriteria optimization framework to seek the optimal operation rules for the existing Feitsui Reservoir system (Taiwan) under various scenarios. The best overall performance is achieved by an optimal dual strategy whose operational parameters are all determined by optimization. The optimal environmental flow target may well be a top-priority constant base flow rather than the variable quantities. The active strategy would outperform the restrictive one. For the former, a top-priority base flow target is essential; for the latter, the off-stream demand can become vanishingly small in compensation for the eliminated base flow target, thus promoting the monthly flow target as nearly the top-priority demand. For either the active or restrictive strategy, a prioritized environmental flow demand would provide a path toward the optimal overall performance. A significantly improved overall performance over the existing operation rules is unlikely if the active and restrictive parameters are both favorable
Examining the Bernstein global optimization approach to optimal power flow problem
NASA Astrophysics Data System (ADS)
Patil, Bhagyesh V.; Sampath, L. P. M. I.; Krishnan, Ashok; Ling, K. V.; Gooi, H. B.
2016-10-01
This work addresses a nonconvex optimal power flow problem (OPF). We introduce a `new approach' in the context of OPF problem based on the Bernstein polynomials. The applicability of the approach is studied on a real-world 3-bus power system. The numerical results obtained with this new approach for a 3-bus system reveal a satisfactory improvement in terms of optimality. The results are found to be competent with generic global optimization solvers BARON and COUENNE.
Modeling flow and transport in unsaturated fractured rock: an evaluation of the continuum approach.
Liu, Hui-Hai; Haukwa, Charles B; Ahlers, C Fredrik; Bodvarsson, Gudmundur S; Flint, Alan L; Guertal, William B
2003-01-01
Because the continuum approach is relatively simple and straightforward to implement, it has been commonly used in modeling flow and transport in unsaturated fractured rock. However, the usefulness of this approach can be questioned in terms of its adequacy for representing fingering flow and transport in unsaturated fractured rock. The continuum approach thus needs to be evaluated carefully by comparing simulation results with field observations directly related to unsaturated flow and transport processes. This paper reports on such an evaluation, based on a combination of model calibration and prediction, using data from an infiltration test carried out in a densely fractured rock within the unsaturated zone of Yucca Mountain, Nevada. Comparisons between experimental and modeling results show that the continuum approach may be able to capture important features of flow and transport processes observed from the test. The modeling results also show that matrix diffusion may have a significant effect on the overall transport behavior in unsaturated fractured rocks, which can be used to estimate effective fracture-matrix interface areas based on tracer transport data. While more theoretical, numerical, and experimental studies are needed to provide a conclusive evaluation, this study suggests that the continuum approach is useful for modeling flow and transport in unsaturated, densely fractured rock.
Modeling flow and transport in unsaturated fractured rock: An evaluation of the continuum approach
Liu, H.-H.; Haukwa, C.B.; Ahlers, C.F.; Bodvarsson, G.S.; Flint, A.L.; Guertal, W.B.
2003-01-01
Because the continuum approach is relatively simple and straightforward to implement, it has been commonly used in modeling flow and transport in unsaturated fractured rock. However, the usefulness of this approach can be questioned in terms of its adequacy for representing fingering flow and transport in unsaturated fractured rock. The continuum approach thus needs to be evaluated carefully by comparing simulation results with field observations directly related to unsaturated flow and transport processes. This paper reports on such an evaluation, based on a combination of model calibration and prediction, using data from an infiltration test carried out in a densely fractured rock within the unsaturated zone of Yucca Mountain, Nevada. Comparisons between experimental and modeling results show that the continuum approach may be able to capture important features of flow and transport processes observed from the test. The modeling results also show that matrix diffusion may have a significant effect on the overall transport behavior in unsaturated fractured rocks, which can be used to estimate effective fracture-matrix interface areas based on tracer transport data. While more theoretical, numerical, and experimental studies are needed to provide a conclusive evaluation, this study suggests that the continuum approach is useful for modeling flow and transport in unsaturated, densely fractured rock. ?? 2002 Elsevier Science B.V. All rights reserved.
Modeling flow and transport in unsaturated fractured rock: An evaluation of the continuum approach
Liu, Hui-Hai; Haukwa, Charles B.; Ahlers, C. Fredrik; Bodvarsson, Gudmundur S.; Flint, Alan L.; Guertal, William B.
2002-09-01
Because the continuum approach is relatively simple and straightforward to implement, it has been commonly used in modeling flow and transport in unsaturated fractured rock. However, the usefulness of this approach can be questioned in terms of its adequacy for representing fingering flow and transport in unsaturated fractured rock. The continuum approach thus needs to be evaluated carefully by comparing simulation results with field observations directly related to unsaturated flow and transport processes. This paper reports on such an evaluation, based on a combination of model calibration and prediction, using data from an infiltration test carried out in a densely fractured rock within the unsaturated zone of Yucca Mountain, Nevada. Comparisons between experimental and modeling results show that the continuum approach may be able to capture important features of flow and transport processes observed from the test. The modeling results also show that matrix diffusion may have a significant effect on the overall transport behavior in unsaturated fractured rocks, which can be used to estimate effective fracture-matrix interface areas based on tracer transport data. While more theoretical, numerical, and experimental studies are needed to provide a conclusive evaluation, this study suggests that the continuum approach is useful for modeling flow and transport in unsaturated, densely fractured rock.
A Biomass Flow Approach to Population Models and Food Webs.
Getz, Wayne M
2012-02-01
The dominant differential equation paradigm for modeling the population dynamics of species interacting in the framework of a food web retains at its core the basic prey-predator and competition models formulation by Alfred J. Lotka (1880-1945) and Vito Volterra (1860-1940) nearly nine decades ago. This paradigm lacks a trophic-level-independent formulation of population growth leading to ambiguities in how to treat populations that are simultaneously both prey and predator. Also, this paradigm does not fundamentally include inertial (i.e. change resisting) processes needed to account for the response of populations to fluctuating resource environments. Here I present an approach that corrects both these deficits and provides a unified framework for accounting for biomass transformation in food webs that include both live and dead components of all species in the system. This biomass transformation formulation (BTW) allows for a unified treatment of webs that include consumers of both live and dead material-both carnivores and carcasivores, herbivores and detritivores-and incorporates scavengers, parasites, and other neglected food web consumption categories in a coherent manner. I trace how BTW is an outgrowth of the metaphysiological growth modeling paradigm and I provide a general compact formulation of BTW in terms of a three-variable differential equation formulation for each species in the food web: viz. live biomass, dead biomass, and a food-intake-related measure called deficit-stress. I then illustrate the application of this new paradigm to provide insights into two-species competition in variable environments and discuss application of BTW to food webs that incorporate parasites and pathogens.
A Biomass Flow Approach to Population Models and Food Webs
Getz, Wayne M.
2011-01-01
The dominant differential equation paradigm for modeling the population dynamics of species interacting in the framework of a food web retains at its core the basic prey-predator and competition models formulation by Alfred J. Lotka (1880–1945) and Vito Volterra (1860–1940) nearly nine decades ago. This paradigm lacks a trophic-level-independent formulation of population growth leading to ambiguities in how to treat populations that are simultaneously both prey and predator. Also, this paradigm does not fundamentally include inertial (i.e. change resisting) processes needed to account for the response of populations to fluctuating resource environments. Here I present an approach that corrects both these deficits and provides a unified framework for accounting for biomass transformation in food webs that include both live and dead components of all species in the system. This biomass transformation formulation (BTW) allows for a unified treatment of webs that include consumers of both live and dead material—both carnivores and carcasivores, herbivores and detritivores—and incorporates scavengers, parasites, and other neglected food web consumption categories in a coherent manner. I trace how BTW is an outgrowth of the metaphysiological growth modeling paradigm and I provide a general compact formulation of BTW in terms of a three-variable differential equation formulation for each species in the food web: viz. live biomass, dead biomass, and a food-intake-related measure called deficit-stress. I then illustrate the application of this new paradigm to provide insights into two-species competition in variable environments and discuss application of BTW to food webs that incorporate parasites and pathogens. PMID:27688596
A Mixed Approach for Modeling Blood Flow in Brain Microcirculation
NASA Astrophysics Data System (ADS)
Peyrounette, M.; Sylvie, L.; Davit, Y.; Quintard, M.
2014-12-01
We have previously demonstrated [1] that the vascular system of the healthy human brain cortex is a superposition of two structural components, each corresponding to a different spatial scale. At small-scale, the vascular network has a capillary structure, which is homogeneous and space-filling over a cut-off length. At larger scale, veins and arteries conform to a quasi-fractal branched structure. This structural duality is consistent with the functional duality of the vasculature, i.e. distribution and exchange. From a modeling perspective, this can be viewed as the superposition of: (a) a continuum model describing slow transport in the small-scale capillary network, characterized by a representative elementary volume and effective properties; and (b) a discrete network approach [2] describing fast transport in the arterial and venous network, which cannot be homogenized because of its fractal nature. This problematic is analogous to modeling problems encountered in geological media, e.g, in petroleum engineering, where fast conducting channels (wells or fractures) are embedded in a porous medium (reservoir rock). An efficient method to reduce the computational cost of fractures/continuum simulations is to use relatively large grid blocks for the continuum model. However, this also makes it difficult to accurately couple both structural components. In this work, we solve this issue by adapting the "well model" concept used in petroleum engineering [3] to brain specific 3-D situations. We obtain a unique linear system of equations describing the discrete network, the continuum and the well model coupling. Results are presented for realistic geometries and compared with a non-homogenized small-scale network model of an idealized periodic capillary network of known permeability. [1] Lorthois & Cassot, J. Theor. Biol. 262, 614-633, 2010. [2] Lorthois et al., Neuroimage 54 : 1031-1042, 2011. [3] Peaceman, SPE J. 18, 183-194, 1978.
A Hybrid URANS/LES Approach Used for Simulations of Turbulent Flows
NASA Astrophysics Data System (ADS)
Fraňa, Karel; Stiller, Jörg
A hybrid model based on the unsteady Reynolds averaged Navier-Stokes approach represented by the one-equation Spalart-Allmaras model and the Large Eddy Simulation called Detached Eddy Simulation (DES) was applied for turbulent flow simulations. This turbulent approach was implemented into the flow solver based on the Finite-Element Method with pressure stabilized and streamlines upwind Petrov-Galerkin stabilization techniques. The effectiveness and robustness of this updated solver is successfully demonstrated at benchmark calculation represented by an unsteady turbulent flow past a cylinder at Reynolds number 3900. Results such as velocity fields and the flow periodicity, Reynolds stress tensor and eddy viscosity and pressure coefficient distributions are discussed and relatively good agreement was found to direct numerical simulations and experiments.
NASA Technical Reports Server (NTRS)
Bey, K. S.; Thornton, E. A.; Dechaumphai, P.; Ramakrishnan, R.
1985-01-01
Recent progress in the development of finite element methodology for the prediction of aerothermal loads is described. Two dimensional, inviscid computations are presented, but emphasis is placed on development of an approach extendable to three dimensional viscous flows. Research progress is described for: (1) utilization of a commercially available program to construct flow solution domains and display computational results, (2) development of an explicit Taylor-Galerkin solution algorithm, (3) closed form evaluation of finite element matrices, (4) vector computer programming strategies, and (5) validation of solutions. Two test problems of interest to NASA Langley aerothermal research are studied. Comparisons of finite element solutions for Mach 6 flow with other solution methods and experimental data validate fundamental capabilities of the approach for analyzing high speed inviscid compressible flows.
NASA Technical Reports Server (NTRS)
Bey, K. S.; Thornton, E. A.; Dechaumphai, P.; Ramakrishnan, R.
1985-01-01
Recent progress in the development of finite element methodology for the prediction of aerothermal loads is described. Two dimensional, inviscid computations are presented, but emphasis is placed on development of an approach extendable to three dimensional viscous flows. Research progress is described for: (1) utilization of a commerically available program to construct flow solution domains and display computational results, (2) development of an explicit Taylor-Galerkin solution algorithm, (3) closed form evaluation of finite element matrices, (4) vector computer programming strategies, and (5) validation of solutions. Two test problems of interest to NASA Langley aerothermal research are studied. Comparisons of finite element solutions for Mach 6 flow with other solution methods and experimental data validate fundamental capabilities of the approach for analyzing high speed inviscid compressible flows.
NASA Technical Reports Server (NTRS)
Glaze, L. S.; Baloga, S. M.
2014-01-01
Pahoehoe lavas are recognized as an important landform on Earth, Mars and Io. Observations of such flows on Earth (e.g., Figure 1) indicate that the emplacement process is dominated by random effects. Existing models for lobate a`a lava flows that assume viscous fluid flow on an inclined plane are not appropriate for dealing with the numerous random factors present in pahoehoe emplacement. Thus, interpretation of emplacement conditions for pahoehoe lava flows on Mars requires fundamentally different models. A new model that implements a simulation approach has recently been developed that allows exploration of a variety of key influences on pahoehoe lobe emplacement (e.g., source shape, confinement, slope). One important factor that has an impact on the final topographic shape and morphology of a pahoehoe lobe is the volumetric flow rate of lava, where cooling of lava on the lobe surface influences the likelihood of subsequent breakouts.
Arbitrary Lagrangian-Eulerian approach in reduced order modeling of a flow with a moving boundary
NASA Astrophysics Data System (ADS)
Stankiewicz, W.; Roszak, R.; Morzyński, M.
2013-06-01
Flow-induced deflections of aircraft structures result in oscillations that might turn into such a dangerous phenomena like flutter or buffeting. In this paper the design of an aeroelastic system consisting of Reduced Order Model (ROM) of the flow with a moving boundary is presented. The model is based on Galerkin projection of governing equation onto space spanned by modes obtained from high-fidelity computations. The motion of the boundary and mesh is defined in Arbitrary Lagrangian-Eulerian (ALE) approach and results in additional convective term in Galerkin system. The developed system is demonstrated on the example of a flow around an oscillating wing.
De Pretto, Lucas R. Nogueira, Gesse E. C.; Freitas, Anderson Z.
2016-04-28
Functional modalities of Optical Coherence Tomography (OCT) based on speckle analysis are emerging in the literature. We propose a simple approach to the autocorrelation of OCT signal to enable volumetric flow rate differentiation, based on decorrelation time. Our results show that this technique could distinguish flows separated by 3 μl/min, limited by the acquisition speed of the system. We further perform a B-scan of gradient flow inside a microchannel, enabling the visualization of the drag effect on the walls.
NASA Astrophysics Data System (ADS)
Babak, Petro; Azaiez, Jalel
2014-12-01
A unified approach to modeling flows of slightly compressible fluids through naturally fractured media is presented. The unified fractional differential model is derived by combining the flow at micro scale for matrix blocks and macro scale for fractures, using the transient interporosity flow behavior at the interface between matrix blocks and fractures. The derived model is able to unify existing transient interporosity flow models formulated for different shapes of matrix blocks in any medium dimensions. The model is formulated in the form of a fractional order partial differential equation that involves Caputo derivative of order 1/2 with respect to time. Explicit solutions for the unified model are derived for different axisymmetrical spatial domains using Hankel or Hankel-Weber finite or infinite transforms. Comparisons between the predictions of the unified model and those obtained from existing transient interporosity flow models for matrix blocks in the form of slabs, spheres and cylinders are presented. It is shown that the unified fractional derivative model leads to solutions that are very close to those of transient interporosity flow models for fracture-dominant and transitional fracture-to-matrix dominant flow regimes. An analysis of the results of the unified model reveals that the pressure varies linearly with the logarithm of time for different flow regimes, with half slope for the transitional fracture-to-matrix dominant flow regime vs. the fracture and matrix dominant flow regimes. In addition, a new re-scaling that involves the characteristic length in the form of matrix block volume to surface area ratio is derived for the transient interporosity flow models for matrix blocks of different shapes. It is shown that the re-scaled transient interporosity flow models are governed by two dimensionless parameters Θ and Λ compared to only one dimensionless parameter Θ for the unified model. It is shown that the solutions of the transient
Multi-compartment approach to identify minimal flow and maximal recreational use of a lowland river
NASA Astrophysics Data System (ADS)
Pusch, Martin; Lorenz, Stefan
2013-04-01
Most approaches to establish a minimum flow rate for river sections subjected to water abstraction focus on flow requirements of fish and benthic invertebrates. However, artificial reduction of river flow will always affect additional key ecosystem features, as sediment properties and the metabolism of matter in these ecosystems as well, and may even influence adjacent floodplains. Thus, significant effects e.g. on the dissolved oxygen content of river water, on habitat conditions in the benthic zone, and on water levels in the floodplain are to be expected. Thus, we chose a multiple compartment method to identify minimum flow requirements in a lowland River in northern Germany (Spree River), selecting the minimal required flow level out of all compartments studied. Results showed that minimal flow levels necessary to keep key ecosystem features at a 'good' state depended significantly on actual water quality and on river channel morphology. Thereby, water quality of the Spree is potentially influenced by recreational boating activity, which causes mussels to stop filter-feeding, and thus impedes self-purification. Disturbance of mussel feeding was shown to directly depend on boat type and speed, with substantial differences among mussel species. Thus, a maximal recreational boating intensity could be derived that does not significantly affect self purification. We conclude that minimal flow levels should be identified not only based on flow preferences of target species, but also considering channel morphology, ecological functions, and the intensity of other human uses of the river section.
Mohebbi-Kalhori, Davod
2011-12-01
Despite the success of hollow-fiber membrane bioreactors in tissue engineering, few evaluations of steady- and pulsatile-flow perfusion through these bioreactors have been made. Such evaluations are vital to the optimization of bioreactor culture conditions. In this study, positron emission tomography (PET) was proposed and used to visualize steady- and pulsatile-flow perfusion in hollow-fiber membrane bioreactors for tissue-engineering applications. PET is a noninvasive method that allows measuring the spatial distribution of a radioactive tracer by detecting its activity within porous scaffolds. A radioactive tracer, 18-fluoro-deoxy-glucose ((18)FDG), was injected into a fluid circuit having a hollow-fiber membrane bioreactor with gel-devoid or gel-filled extracapillary space. Dynamic PET scans of the inlet section were acquired and followed by volumetric PET scans of the whole bioreactor. Results were used to reconstruct dynamic and volumetric two- and three-dimensional images. Pulsatile inlet flow improved the uniformity of perfusion flow within the bioreactor in comparison to the steady inlet flow. Pulsatile flow also reduced the accumulation of radioactive tracer for both gel-devoid and gel-filled bioreactors compared to the steady flow. The stability of the radioactive tracer for both conditions was evaluated. The potential of the PET approach was demonstrated by the quantification of the imaging results for steady- and pulsatile-flow perfusions that can be used for the development of bioreactors for tissue-engineering applications.
A fully automated flow-based approach for accelerated peptide synthesis.
Mijalis, Alexander J; Thomas, Dale A; Simon, Mark D; Adamo, Andrea; Beaumont, Ryan; Jensen, Klavs F; Pentelute, Bradley L
2017-05-01
Here we report a fully automated, flow-based approach to solid-phase polypeptide synthesis, with amide bond formation in 7 seconds and total synthesis times of 40 seconds per amino acid residue. Crude peptide purities and isolated yields were comparable to those for standard-batch solid-phase peptide synthesis. At full capacity, this approach can yield tens of thousands of individual 30-mer peptides per year.
A new approach to flow through a region bounded by two ellipses of the same ellipticity
NASA Astrophysics Data System (ADS)
Lal, K.; Chorlton, F.
1981-05-01
A new approach is presented to calculate steady flow of a laminar viscous incompressible fluid through a channel whose cross section is bounded by two ellipses with the same ellipticity. The Milne-Thomas approach avoids the stream function and is similar to the Rayleigh-Ritz approximation process of the calculus of variations in its first satisfying boundary conditions and then adjusting constants or multiplying functions to fit the differential equation.
Quantifying Aeolian Flow-Landform Interactions Using Novel Lab-Scale Experimental Approaches
NASA Astrophysics Data System (ADS)
Christensen, K. T.; Bristow, N.; Hamed, A. M.; Kim, T.; Blois, G.; Best, J.
2016-12-01
Aeolian transport processes are driven by coupled interactions of flow with complex and dynamic topography. The complexity of this coupling inhibits predictions of sediment transport, landscape morphodynamics and concomitant biophysical and geochemical processes. Many of these flows occur in conditions and/or at scales that limit or completely impede access via modern flow diagnostics due to geometry and/or coexistence of multiple phases. Given the broad range of scales of such flows, modeling at small scales is required to enable predictive simulations. It is at these scales where experiments can inform model development that accurately reflect the physics of such processes to yield reliable system-scale predictions. This lecture will highlight specific two laboratory studies: turbulent flow associated with interacting barchan dunes and the flow overlying a model crater representative of that observed on Mars. The evolution of and dynamics associated with barchan dunes involve a strong degree of coupling between sediment transport, morphological change, and flow, the last of which represents the weakest link in our understanding of barchan morphodynamics. Newly available morphological data from high-resolution images from orbiting NASA spacecraft, complemented by on-site observations, is supporting the paleoscientific reconstruction of Mars environmental conditions. Central to this goal is understanding the geomorphology of Mars craters, including morphological processes that control their evolution for those that host a central mound. The 3D nature of both landforms presents challenges for measuring the full flow field. We therefore utilize a novel refractive index matching (RIM) approach coupled with particle-image velocimetry (PIV) methods to fully interrogate the flow around fixed barchan dune models in tandem and a crater model formed from a DEM of Gale Crater. The barchan and crater models were fabricated from acrylic whose refractive index matches the
A Vocabulary Approach to Partial Streamline Matching and Exploratory Flow Visualization.
Tao, Jun; Wang, Chaoli; Shene, Ching-Kuang; Shaw, Raymond A
2016-05-01
Measuring the similarity of integral curves is fundamental to many important flow data analysis and visualization tasks such as feature detection, pattern querying, streamline clustering, and hierarchical exploration. In this paper, we introduce FlowString, a novel vocabulary approach that extracts shape invariant features from streamlines and utilizes a string-based method for exploratory streamline analysis and visualization. Our solution first resamples streamlines by considering their local feature scales. We then classify resampled points along streamlines based on the shape similarity around their local neighborhoods. We encode each streamline into a string of well-selected shape characters, from which we construct meaningful words for querying and retrieval. A unique feature of our approach is that it captures intrinsic streamline similarity that is invariant under translation, rotation and scaling. We design an intuitive interface and user interactions to support flexible querying, allowing exact and approximate searches for partial streamline matching. Users can perform queries at either the character level or the word level, and define their own characters or words conveniently for customized search. We demonstrate the effectiveness of FlowString with several flow field data sets of different sizes and characteristics. We also extend FlowString to handle multiple data sets and perform an empirical expert evaluation to confirm the usefulness of this approach.
Analyzing Unsatirated Flow Patterns in Fractured Rock Using an Integrated Modeling Approach
Y.S. Wu; G. Lu; K. Zhang; L. Pan; G.S. Bodvarsson
2006-08-03
Characterizing percolation patterns in unsaturated fractured rock has posed a greater challenge to modeling investigations than comparable saturated zone studies, because of the heterogeneous nature of unsaturated media and the great number of variables impacting unsaturated flow. This paper presents an integrated modeling methodology for quantitatively characterizing percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The modeling approach integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model for modeling analyses. It takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain's highly heterogeneous, unsaturated fractured tuffs. Modeling results are examined against different types of field-measured data and then used to evaluate different hydrogeological conceptualizations and their results of flow patterns in the unsaturated zone. In particular, this model provides a much clearer understanding of percolation patterns and flow behavior through the unsaturated zone, both crucial issues in assessing repository performance. The integrated approach for quantifying Yucca Mountain's flow system is demonstrated to provide a practical modeling tool for characterizing flow and transport processes in complex subsurface systems.
NASA Astrophysics Data System (ADS)
Chigullapalli, Sruti
Micro-electro-mechanical systems (MEMS) are widely used in automotive, communications and consumer electronics applications with microactuators, micro gyroscopes and microaccelerometers being just a few examples. However, in areas where high reliability is critical, such as in aerospace and defense applications, very few MEMS technologies have been adopted so far. Further development of high frequency microsystems such as resonators, RF MEMS, microturbines and pulsed-detonation microengines require improved understanding of unsteady gas dynamics at the micro scale. Accurate computational simulation of such flows demands new approaches beyond the conventional formulations based on the macroscopic constitutive laws. This is due to the breakdown of the continuum hypothesis in the presence of significant non-equilibrium and rarefaction because of large gradients and small scales, respectively. More generally, the motion of molecules in a gas is described by the kinetic Boltzmann equation which is valid for arbitrary Knudsen numbers. However, due to the multidimensionality of the phase space and the complex non-linearity of the collision term, numerical solution of the Boltzmann equation is challenging for practical problems. In this thesis a fully deterministic, as opposed to a statistical, finite volume based three-dimensional solution of Boltzmann ES-BGK model kinetic equation is formulated to enable simulations of unsteady rarefied flows. The main goal of this research is to develop an unsteady rarefied solver integrated with finite volume method (FVM) solver in MEMOSA (MEMS Overall Simulation Administrator) developed by PRISM: NNSA center for Prediction of Reliability, Integrity and Survivability of Microsystems (PRISM) at Purdue and apply it to study micro-scale gas damping. Formulation and verification of finite volume method for unsteady rarefied flow solver based on Boltzmann-ESBGK equations in arbitrary three-dimensional geometries are presented. The solver is
Wu, Yu-Shu; Lu, Guoping; Zhang, Keni; Pan, Lehua; Bodvarsson,Gudmundur S.
2003-11-03
This paper presents a series of modeling investigations to characterize percolation patterns in the unsaturated zone of Yucca Mountain, Nevada, a proposed underground repository site for storing high-level radioactive waste. The investigations are conducted using a modeling approach that integrates a wide variety of moisture, pneumatic, thermal, and isotopic geochemical field data into a comprehensive three-dimensional numerical model through model calibration. This integrated modeling approach, based on a dual-continuum formulation, takes into account the coupled processes of fluid and heat flow and chemical isotopic transport in Yucca Mountain's highly heterogeneous, unsaturated fractured tuffs. In particular, the model results are examined against different types of field-measured data and used to evaluate different hydrogeological conceptual models and their effects on flow patterns in the unsaturated zone. The objective of this work to provide understanding of percolation patterns and flow behavior through the unsaturated zone, which is a crucial issue in assessing repository performance.
Innovative Approaches for Urban Watershed Wet-Weather Flow Management and Control
The “Innovative Approaches for Urban Watershed Wet-Weather Flow Management and Control: State of the Technology” project investigated a range of innovative technology and management strategies emerging outside the normal realm of business within the continental United States, fo...
Improving Joint Expeditionary Medical Planning Tools Based on a Patient Flow Approach
2012-01-01
considers neither the significant daily variability observed in histori - 1 A patient condition code is a standardized coding scheme that contains a...Medical Planning Tools Based on a Patient Flow Approach wounds become infected, including with tetanus .9 The high incidence of infected wounds may...2004) Hurricane Katrina (2005) Kashmir earthquake (2005) Fracture Puncture Strain/sprain Laceration Tetanus vaccination Distribution (%) 70
Detailed Model Study of Pump-Approach Flows for the Lake Chicot Pumping Plant,
1977-10-01
in the trash -rack tests, and an extensive study was conducted to obtain an improved sump configuration which would minimize any vortex -related...velocity resulted from geometric constraints imposed on the plant configuration. In order to achieve better pump approach-flow conditions trash racks with...and a floor mounted splitter plate ( vortex breaker) beneath the pump. (Author)
NASA Technical Reports Server (NTRS)
Sidilkover, David
1997-01-01
Some important advances took place during the last several years in the development of genuinely multidimensional upwind schemes for the compressible Euler equations. In particular, a robust, high-resolution genuinely multidimensional scheme which can be used for any of the flow regimes computations was constructed. This paper summarizes briefly these developments and outlines the fundamental advantages of this approach.
Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow
ERIC Educational Resources Information Center
Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan
2012-01-01
In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms…
ERIC Educational Resources Information Center
Djelic, Marina; Mazic, Sanja; Zikic, Dejan
2013-01-01
In the frame of a laboratory training course for medicine students, a new approach for laboratory exercises has been applied to teach the phenomena of circulation. The exercise program included measurements of radial artery blood flow waveform for different age groups using a noninvasive optical sensor. Arterial wave reflection was identified by…
Innovative Approaches for Urban Watershed Wet-Weather Flow Management and Control
The “Innovative Approaches for Urban Watershed Wet-Weather Flow Management and Control: State of the Technology” project investigated a range of innovative technology and management strategies emerging outside the normal realm of business within the continental United States, fo...
ERIC Educational Resources Information Center
Djelic, Marina; Mazic, Sanja; Zikic, Dejan
2013-01-01
In the frame of a laboratory training course for medicine students, a new approach for laboratory exercises has been applied to teach the phenomena of circulation. The exercise program included measurements of radial artery blood flow waveform for different age groups using a noninvasive optical sensor. Arterial wave reflection was identified by…
A new approach for flow-through respirometry measurements in humans
Ingebrigtsen, Jan P.; Bergouignan, Audrey; Ohkawara, Kazunori; Kohrt, Wendy M.; Lighton, John R. B.
2010-01-01
Indirect whole room calorimetry is commonly used in studies of human metabolism. These calorimeters can be configured as either push or pull systems. A major obstacle to accurately calculating gas exchange rates in a pull system is that the excurrent flow rate is increased above the incurrent flow rate, because the organism produces water vapor, which also dilutes the concentrations of respiratory gasses in the excurrent sample. A common approach to this problem is to dry the excurrent gasses prior to measurement, but if drying is incomplete, large errors in the calculated oxygen consumption will result. The other major potential source of error is fluctuations in the concentration of O2 and CO2 in the incurrent airstream. We describe a novel approach to measuring gas exchange using a pull-type whole room indirect calorimeter. Relative humidity and temperature of the incurrent and excurrent airstreams are measured continuously using high-precision, relative humidity and temperature sensors, permitting accurate measurement of water vapor pressure. The excurrent flow rates are then adjusted to eliminate the flow contribution from water vapor, and respiratory gas concentrations are adjusted to eliminate the effect of water vapor dilution. In addition, a novel switching approach is used that permits constant, uninterrupted measurement of the excurrent airstream while allowing frequent measurements of the incurrent airstream. To demonstrate the accuracy of this approach, we present the results of validation trials compared with our existing system and metabolic carts, as well as the results of standard propane combustion tests. PMID:20200135
Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow
ERIC Educational Resources Information Center
Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan
2012-01-01
In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms…
A knowledge-based approach to automated flow-field zoning for computational fluid dynamics
NASA Technical Reports Server (NTRS)
Vogel, Alison Andrews
1989-01-01
An automated three-dimensional zonal grid generation capability for computational fluid dynamics is shown through the development of a demonstration computer program capable of automatically zoning the flow field of representative two-dimensional (2-D) aerodynamic configurations. The applicability of a knowledge-based programming approach to the domain of flow-field zoning is examined. Several aspects of flow-field zoning make the application of knowledge-based techniques challenging: the need for perceptual information, the role of individual bias in the design and evaluation of zonings, and the fact that the zoning process is modeled as a constructive, design-type task (for which there are relatively few examples of successful knowledge-based systems in any domain). Engineering solutions to the problems arising from these aspects are developed, and a demonstration system is implemented which can design, generate, and output flow-field zonings for representative 2-D aerodynamic configurations.
Computation of Sound Generated by Flow Over a Circular Cylinder: An Acoustic Analogy Approach
NASA Technical Reports Server (NTRS)
Brentner, Kenneth S.; Cox, Jared S.; Rumsey, Christopher L.; Younis, Bassam A.
1997-01-01
The sound generated by viscous flow past a circular cylinder is predicted via the Lighthill acoustic analogy approach. The two dimensional flow field is predicted using two unsteady Reynolds-averaged Navier-Stokes solvers. Flow field computations are made for laminar flow at three Reynolds numbers (Re = 1000, Re = 10,000, and Re = 90,000) and two different turbulent models at Re = 90,000. The unsteady surface pressures are utilized by an acoustics code that implements Farassat's formulation 1A to predict the acoustic field. The acoustic code is a 3-D code - 2-D results are found by using a long cylinder length. The 2-D predictions overpredict the acoustic amplitude; however, if correlation lengths in the range of 3 to 10 cylinder diameters are used, the predicted acoustic amplitude agrees well with experiment.
Flow equation approach to one-body and many-body localization
NASA Astrophysics Data System (ADS)
Quito, Victor; Bhattacharjee, Paraj; Pekker, David; Refael, Gil
2014-03-01
We study one-body and many-body localization using the flow equation technique applied to spin-1/2 Hamiltonians. This technique, first introduced by Wegner, allows us to exact diagonalize interacting systems by solving a set of first-order differential equations for coupling constants. Besides, by the flow of individual operators we also compute physical properties, such as correlation and localization lengths, by looking at the flow of probability distributions of couplings in the Hilbert space. As a first example, we analyze the one-body localization problem written in terms of spins, the disordered XY model with a random transverse field. We compare the results obtained in the flow equation approach with the diagonalization in the fermionic language. For the many-body problem, we investigate the physical properties of the disordered XXZ Hamiltonian with a random transverse field in the z-direction.
Issues and approach to develop validated analysis tools for hypersonic flows: One perspective
NASA Technical Reports Server (NTRS)
Deiwert, George S.
1992-01-01
Critical issues concerning the modeling of low-density hypervelocity flows where thermochemical nonequilibrium effects are pronounced are discussed. Emphasis is on the development of validated analysis tools. A description of the activity in the Ames Research Center's Aerothermodynamics Branch is also given. Inherent in the process is a strong synergism between ground test and real-gas computational fluid dynamics (CFD). Approaches to develop and/or enhance phenomenological models and incorporate them into computational flow-field simulation codes are discussed. These models have been partially validated with experimental data for flows where the gas temperature is raised (compressive flows). Expanding flows, where temperatures drop, however, exhibit somewhat different behavior. Experimental data for these expanding flow conditions are sparse; reliance must be made on intuition and guidance from computational chemistry to model transport processes under these conditions. Ground-based experimental studies used to provide necessary data for model development and validation are described. Included are the performance characteristics of high-enthalpy flow facilities, such as shock tubes and ballistic ranges.
NASA Astrophysics Data System (ADS)
Delay, Frederick; Porel, Gilles; Chatelier, Marion
2013-07-01
We present a modeling exercise of solute transport and biodegradation in a coarse porous medium widely colonized by a biofilm phase. Tracer tests in large laboratory columns using both conservative (fluorescein) and biodegradable (nitrate) solutes are simulated by means of a dual flowing continuum approach. The latter clearly distinguishes concentrations in a flowing porous phase from concentrations conveyed in the biofilm. With this conceptual setting, it becomes possible to simulate the sharp front of concentrations at early times and the flat tail of low concentrations at late times observed on the experimental breakthrough curves. Thanks to the separation of flow in two phases at different velocities, dispersion coefficients in both flowing phases keep reasonable values with some physical meaning. This is not the case with simpler models based on a single continuum (eventually concealing dead-ends), for which inferred dispersivity may reach the unphysical value of twice the size of the columns. We also show that the behavior of the dual flowing continuum is mainly controlled by the relative fractions of flow passing in each phase and the rate of mass transfer between phases. These parameters also condition the efficiency of nitrate degradation, the degradation rate in a well-seeded medium being a weakly sensitive parameter. Even though the concept of dual flowing continuum appears promising for simulating transport in complex porous media, its inversion onto experimental data really benefits from attempts with simpler models providing a rough pre-evaluation of parameters such as porosity and mean fluid velocity in the system.
River flow forecasting: use of phase-space reconstruction and artificial neural networks approaches
NASA Astrophysics Data System (ADS)
Sivakumar, B.; Jayawardena, A. W.; Fernando, T. M. K. G.
2002-08-01
The use of two non-linear black-box approaches, phase-space reconstruction (PSR) and artificial neural networks (ANN), for forecasting river flow dynamics is studied and a comparison of their performances is made. This is done by attempting 1-day and 7-day ahead forecasts of the daily river flow from the Nakhon Sawan station at the Chao Phraya River basin in Thailand. The results indicate a reasonably good performance of both approaches for both 1-day and 7-day ahead forecasts. However, the performance of the PSR approach is found to be consistently better than that of ANN. One reason for this could be that in the PSR approach the flow series in the phase-space is represented step by step in local neighborhoods, rather than a global approximation as is done in ANN. Another reason could be the use of the multi-layer perceptron (MLP) in ANN, since MLPs may not be most appropriate for forecasting at longer lead times. The selection of training set for the ANN may also contribute to such results. A comparison of the optimal number of variables for capturing the flow dynamics, as identified by the two approaches, indicates a large discrepancy in the case of 7-day ahead forecasts (1 and 7 variables, respectively), though for 1-day ahead forecasts it is found to be consistent (3 variables). A possible explanation for this could be the influence of noise in the data, an observation also made from the 1-day ahead forecast results using the PSR approach. The present results lead to observation on: (1) the use of other neural networks for runoff forecasting, particularly at longer lead times; (2) the influence of training set used in the ANN; and (3) the effect of noise on forecast accuracy, particularly in the PSR approach.
Linking river flow regimes to riparian plant guilds: a community-wide modeling approach.
Lytle, David A; Merritt, David M; Tonkin, Jonathan D; Olden, Julian D; Reynolds, Lindsay V
2017-03-06
Modeling riparian plant dynamics along rivers is complicated by the fact that plants have different edaphic and hydrologic requirements at different life-stages. With intensifying human demands for water and continued human alteration of rivers, there is a growing need for predicting responses of vegetation to flow alteration, including responses related to climate change and river flow management. We developed a coupled structured population model that coombines stage-specific responses of plant guilds with specific attributes of river hydrologic regime. The model uses information on the vital rates of guilds as they relate to different hydrologic conditions (flood, drought, and baseflow), but deliberately omits biotic interactions from the structure ("interaction neutral"). Our intent was to: 1) consolidate key vital rates concerning plant population dynamics and to incorporate these data into a quantitative framework, 2) determine whether complex plant stand dynamics, including biotic interactions, can be predicted from basic vital rates and river hydrology, and 3) project how altered flow regimes might affect riparian communities. We illustrated the approach using five flow-response guilds that encompass much of the river floodplain community: hydroriparian tree, xeroriparian shrub, hydroriparian shrub, mesoriparian meadow, and desert shrub. We also developed novel network-based tools for predicting community-wide effects of climate-driven shifts and deliberately altered flow regimes. The model recovered known patterns of hydroriparian tree vs. xeroriparian shrub dominance, including the relative proportion of these two guilds as a function of river flow modification. By simulating flow alteration scenarios ranging from increased drought to shifts in flood timing, the model predicted that mature hydroriparian forest should be most abundant near the observed natural flow regime. Multiguild sensitivity analysis identified substantial network connectivity (many
NASA Astrophysics Data System (ADS)
Zacny, K.; Nagihara, S.; Hedlund, M.; Paulsen, G.; Shasho, J.; Mumm, E.; Kumar, N.; Szwarc, T.; Chu, P.; Craft, J.; Taylor, P.; Milam, M.
2013-11-01
In this paper, the development of heat flow probes for measuring the geothermal gradient and conductivity of lunar regolith are presented. These two measurements are the required information for determining the heat flow of a planetary body. Considering the Moon as an example, heat flow properties are very important information for studying the radiogenic isotopes, the thermal evolution and differentiation history, and the mechanical properties of the interior. In order to obtain the best measurements, the sensors must be extended to a depth of at least 3 m, i.e. beyond the depth of significant thermal cycles. Two approaches to heat flow deployment and measurement are discussed in this paper: a percussive approach and a pneumatic approach. The percussive approach utilizes a high frequency hammer to drive a cone penetrometer into the lunar simulant. Ring-like thermal sensors (heaters and temperature sensors) on the penetrometer rod are deployed into the simulant every 30 cm as the penetrometer penetrates to the required 3 m depth. Once the target depth has been achieved, the deployment rod is removed from the simulant, eliminating any thermal path to the lander. The pneumatic approach relies on pressurized gas to excavate, using a cone-shaped nozzle to penetrate the simulant. The nozzle is attached to a coiled stem with thermal sensors embedded along the length of the stem. As the simulant is being lofted out of the hole by the escaping gas, the stem is progressively reeled out from a spool, thus moving the cone deeper into the hole. Thermal conductivity is measured using a needle probe attached to the end of the cone. Breadboard prototypes of these two heat flow probe systems have been constructed and successfully tested under lunar-like conditions to approximately 70 cm, which was the maximum possible depth allowed by the size of the test bin and the chamber.
Eulerian Mapping Closure Approach for Probability Density Function of Concentration in Shear Flows
NASA Technical Reports Server (NTRS)
He, Guowei; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
The Eulerian mapping closure approach is developed for uncertainty propagation in computational fluid mechanics. The approach is used to study the Probability Density Function (PDF) for the concentration of species advected by a random shear flow. An analytical argument shows that fluctuation of the concentration field at one point in space is non-Gaussian and exhibits stretched exponential form. An Eulerian mapping approach provides an appropriate approximation to both convection and diffusion terms and leads to a closed mapping equation. The results obtained describe the evolution of the initial Gaussian field, which is in agreement with direct numerical simulations.
NASA Astrophysics Data System (ADS)
Mott Lacroix, Kelly E.; Xiu, Brittany C.; Megdal, Sharon B.
2016-04-01
Despite increased understanding of the science of environmental flows, identification and implementation of effective environmental flow policies remains elusive. Perhaps the greatest barrier to implementing flow policies is the framework for water management. An alternative management approach is needed when legal rights for environmental flows do not exist, or are ineffective at protecting ecosystems. The research presented here, conducted in the U.S. state of Arizona, provides an empirical example of engagement to promote social learning as an approach to finding ways to provide water for the environment where legal rights for environmental flows are inadequate. Based on our engagement process we propose that identifying and then building common ground require attention to the process of analyzing qualitative data and the methods for displaying complex information, two aspects not frequently discussed in the social learning or stakeholder engagement literature. The results and methods from this study can help communities develop an engagement process that will find and build common ground, increase stakeholder involvement, and identify innovative solutions to provide water for the environment that reflect the concerns of current water users.
Xu, Tianfu; Pruess, Karsten
2000-08-08
Reactive fluid flow and geochemical transport in unsaturated fractured rocks has received increasing attention for studies of contaminant transport, groundwater quality, waste disposal, acid mine drainage remediation, mineral deposits, sedimentary diagenesis, and fluid-rock interactions in hydrothermal systems. This paper presents methods for modeling geochemical systems that emphasize: (1) involvement of the gas phase in addition to liquid and solid phases in fluid flow, mass transport and chemical reactions, (2) treatment of physically and chemically heterogeneous and fractured rocks, (3) the effect of heat on fluid flow and reaction properties and processes, and (4) the kinetics of fluid-rock interaction. The physical and chemical process model is embodied in a system of partial differential equations for flow and transport, coupled to algebraic equations and ordinary differential equations for chemical interactions. For numerical solution, the continuum equations are discretized in space and time. Space discretization is based on a flexible integral finite difference approach that can use irregular gridding to model geologic structure; time is discretized fully implicitly as a first-order finite difference. Heterogeneous and fractured media are treated with a general multiple interacting continua method that includes double-porosity, dual-permeability, and multi-region models as special cases. A sequential iteration approach is used to treat the coupling between fluid flow and mass transport on the one hand, chemical reactions on the other. Applications of the methods developed here to variably saturated geochemical systems are presented in a companion paper (part 2, this issue).
Mott Lacroix, Kelly E; Xiu, Brittany C; Megdal, Sharon B
2016-04-01
Despite increased understanding of the science of environmental flows, identification and implementation of effective environmental flow policies remains elusive. Perhaps the greatest barrier to implementing flow policies is the framework for water management. An alternative management approach is needed when legal rights for environmental flows do not exist, or are ineffective at protecting ecosystems. The research presented here, conducted in the U.S. state of Arizona, provides an empirical example of engagement to promote social learning as an approach to finding ways to provide water for the environment where legal rights for environmental flows are inadequate. Based on our engagement process we propose that identifying and then building common ground require attention to the process of analyzing qualitative data and the methods for displaying complex information, two aspects not frequently discussed in the social learning or stakeholder engagement literature. The results and methods from this study can help communities develop an engagement process that will find and build common ground, increase stakeholder involvement, and identify innovative solutions to provide water for the environment that reflect the concerns of current water users.
A boundary element approach to estimate the free surface in stratified two-phase flow
NASA Astrophysics Data System (ADS)
Ren, Shangjie; Dong, Feng; Tan, Chao; Xu, Yaoyuan
2012-10-01
Two-phase flows widely exist in many industries. Measuring the phase distribution in two-phase flow is important for the optimization and control of some industrial processes. Electrical resistance tomography (ERT) is a promising non-intrusive visualization technique for monitoring the two-phase flow. However, due to its nonlinear and ill-posed character, high-quality image reconstruction is difficult and some iterative approach is time consuming. In this paper, a boundary element approach is presented for directly estimating the free-surface in two-phase flow using ERT. The unknown free surface is parameterized by a Bézier curve. Coefficients of its control points are estimated by minimizing a residual function using the iterative Levenberg-Marquardt method. To speed up the estimation process, the physical model of ERT is formulated using a boundary element method. Based on this formulation, the forward problem is fast solved through a small size system matrix and the Jacobian matrix is efficiently calculated using an analytic method. After several numerical experiments, this approach is proved fast and precise and several factors influencing the estimation quality are analyzed based on these simulations.
Simulations of Injection, Mixing, and Combustion in Supersonic Flow Using a Hybrid RANS/LES Approach
NASA Astrophysics Data System (ADS)
Peterson, David Michael
There is a great need for accurate and reliable numerical simulation of injection, mixing, and combustion in supersonic combustion ramjet engines. This study seeks to improve the accuracy and reliability which these flow can be simulated with by investigating the use of recent improvements in turbulence modeling and numerical methods. The present numerical simulations use implicit time integration and low-dissipation flux evaluation schemes in an unstructured grid framework. A hybrid Reynolds-Averaged Navier-Stokes and large-eddy simulation approach is used to model turbulence. The large-scale turbulent structure of the flow is resolved, while the near-wall structure is fully modeled. The effects of numerics, grid resolution, and boundary conditions are investigated. The simulation approach is thoroughly validated against available experimental data at a variety of flow conditions. The simulations focus on the injection of fuel through circular injector ports that are oriented either normal to the supersonic crossflow, or at a low angle with respect to the crossflow. The instantaneous flow structure resolved by the simulations is qualitatively compared to experimental flowfield visualization. Quantitative comparisons are made to mean wall pressure, mean velocity, turbulence quantities, and mean mixing data. The simulations are found to do very well at predicting the mean flowfield as well as fluctuations in velocity and injectant concentration. The simulation approach is then used to simulate the flow within a model supersonic combustor. The focus is on the non-reacting case. The simulation results are found to agree well with experimental measurements of temperature and species concentrations. The flow is examined to improve understanding of the mixing within the model combustor. Preliminary results for a simulation including hydrogen combustion are also presented.
NASA Astrophysics Data System (ADS)
Garbin, Silvia; Alessi Celegon, Elisa; Fanton, Pietro; Botter, Gianluca
2017-04-01
The temporal variability of river flow regime is a key feature structuring and controlling fluvial ecological communities and ecosystem processes. In particular, streamflow variability induced by climate/landscape heterogeneities or other anthropogenic factors significantly affects the connectivity between streams with notable implication for river fragmentation. Hydrologic connectivity is a fundamental property that guarantees species persistence and ecosystem integrity in riverine systems. In riverine landscapes, most ecological transitions are flow-dependent and the structure of flow regimes may affect ecological functions of endemic biota (i.e., fish spawning or grazing of invertebrate species). Therefore, minimum flow thresholds must be guaranteed to support specific ecosystem services, like fish migration, aquatic biodiversity and habitat suitability. In this contribution, we present a probabilistic approach aiming at a spatially-explicit, quantitative assessment of hydrologic connectivity at the network-scale as derived from river flow variability. Dynamics of daily streamflows are estimated based on catchment-scale climatic and morphological features, integrating a stochastic, physically based approach that accounts for the stochasticity of rainfall with a water balance model and a geomorphic recession flow model. The non-exceedance probability of ecologically meaningful flow thresholds is used to evaluate the fragmentation of individual stream reaches, and the ensuing network-scale connectivity metrics. A multi-dimensional Poisson Process for the stochastic generation of rainfall is used to evaluate the impact of climate signature on reach-scale and catchment-scale connectivity. The analysis shows that streamflow patterns and network-scale connectivity are influenced by the topology of the river network and the spatial variability of climatic properties (rainfall, evapotranspiration). The framework offers a robust basis for the prediction of the impact of
Unsteady flows of a micropolar fluid between parallel plates using state space approach
NASA Astrophysics Data System (ADS)
Devakar, M.; Iyengar, T. K. V.
2013-04-01
In this paper, we investigate the unsteady flow of an incompressible micropolar fluid between infinite parallel plates using state space approach when one of the plates is set to move suddenly while the other is at rest. Analytical expressions of the fluid velocity and microrotation are obtained in the Laplace transform domain. A standard numerical inversion technique is used to invert the Laplace transform of the velocity and microrotation. The effect of various material parameters on flow variables is discussed and the results are presented through graphs.
Electrification : A New Approach To Evaluate Slip Velocity During Flow Instabilities
NASA Astrophysics Data System (ADS)
Flores, Fabrice; Allal, Ahmed; Guerret-Piècourt, Christelle
2007-04-01
The original feature of this work consists in the parallel study, in extrusion, of the polymer electrification and flow instabilities. On one hand, the Mhetar and Archer model has been used to predict the evolution of slip velocity versus shear stress and on the other hand, the double layer theory seem to be the better theory to explain electrification. We have shown that electrification measurements allow us to measure the slip velocity. The slip velocity values calculated via double layer theory are consistent with those calculated with the Methar and Archer model and allow us to validate our approach. The conclusion is that it's possible to determine the slip velocity during flow instabilities.
Analysis of Different Approaches to Modeling of Nozzle Flows in the Near Continuum Regime (Preprint)
2008-07-07
of Nozzle Flows in the Near Continuum Regime (Preprint) 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) E.V. Titov , Rakesh Kumar...Different Approaches to Modeling of Nozzle Flows in the Near Continuum Regime E. V. Titov , Rakesh Kumar, D. A. Levin∗ and N. E. Gimelshein, S. F...Axisymmetric Geometries, Journal of Computational Physics, Vol. 162, 2000, pp. 429-466. 13. Titov , E.V., and Levin, D.A., Extension of the DSMC method to
High-energy ions produced by two approaching flow fronts in the magnetotail
NASA Astrophysics Data System (ADS)
Uchino, H.; Ieda, A.; Machida, S.; Imada, S.
2015-12-01
During a substorm event in 2009, THEMIS probes observed high-energy (≲ 1MeV) ions and characteristic time evolution of the differential flux. The high-energy ions seem to be produced in the magnetotail, but existing acceleration theories cannot explain the production of such high-energy ions due to the limitation of dawn-dusk (DD) flow scale. We propose that if two approaching flow fronts exist simultaneously in the magnetotail, the production of high-energy ions can be achieved. Namely, some ideal ions are repeatedly reflected by the two fronts and accelerated to high energies, exceeding the energy-limit given by the product of the duskward electric field and DD scale length of the flows. In addition, this acceleration model similar to "first-order Fermi acceleration" can produce the observed differential flux change. We have analytically calculated the energy-gain of each ion between two approaching flow fronts, and roughly estimated the efficiency of the acceleration and the spectrum change. In order to include the DD flow scale, we have further performed a spatially 1-D (2-D in velocity) test particle simulation where a couple of flow fronts approach each other. Using the simulation, we have confirmed the production of high-energy ions as well as the change of the energy spectrum of ions associated with the acceleration. The simulation result shows that high-energy ions can be produced with shorter DD scale length compared to that of the simple acceleration for trapped particles in the flow front. If we assume that the DD scale length of the flow is 10Re, the simulated ion maximum energy near 1MeV and differential flux change are similar to those of the observation. This scale length is less than half of the length needed for the product with the duskward electric field to produce 1MeV ions. This estimated 10Re flow scale in that event does not contradict previous studies.
A computational approach for flow-acoustic coupling in closed side branches.
Radavich, P M; Selamet, A; Novak, J M
2001-04-01
The quarter-wave resonator, which produces a narrow band of high acoustic attenuation at regularly spaced frequency intervals, is a common type of silencer used in ducts. The presence of mean flow in the main duct, however, is likely to promote an interaction between these acoustic resonances and the flow. The coupling for some discrete flow conditions leads to the production of both large wave amplitudes in the side branch and high noise levels in the main duct, thereby transforming the quarter-wave silencer into a noise generator. The present approach employs computational fluid dynamics (CFD) to model this complex interaction between the flow and acoustic resonances at low Mach number by solving the unsteady, turbulent, and compressible Navier-Stokes equations. Comparisons between the present computations and the experiments of Ziada [PVP-Vol. 258, ASME, 35-59 (1993)] for a system with two coaxial side branches show that the method is capable of reproducing the physics of the flow-acoustic coupling and predicting the flow conditions when the coupling occurs. The theory of Howe [IMA J. Appl. Math. 32, 187-209 (1984)] is then employed to determine the location and timing of the acoustic power production during a cycle.
Modelling forces and flow features in flapping wings: a POD based approach
NASA Astrophysics Data System (ADS)
Raiola, Marco; Discetti, Stefano; Ianiro, Andrea
2016-11-01
A novel POD-based approach to decompose the aerodynamic forces acting on a flapping wing along with the most relevant flow features is proposed. The method is applied to experimental data including PIV and force measurements at Re = 3600 and St = 0 . 2 . An actuated 2D flapping wing with a NACA 0012 airfoil is designed to produce independent heaving and pitching motion. The wing is equipped with a 6 Degrees-Of-Freedom balance, providing aerodynamic force measurements. Planar PIV measurements are carried out to obtain a phase-locked flow features description in the wing near field. The PIV phase-averaged flow fields are transformed into flow fields in the reference frame fixed with respect to the moving wing. The POD performed on the vorticity field provides a time basis, constituted by the vorticity time coefficients, on which it is possible to project both the flow fields and the forces in order to assess the force contribution of each POD mode. The force generation is mostly ascribed to the first 4 modes. A satisfactory description of the measured forces is achieved through a truncation to the first 6 modes. A more detailed analysis of the flow field projections is useful to determine the force generation mechanism. This work has been supported by the Spanish MINECO under Grant TRA2013-41103-P.
Schad, A.; Timmer, J.; Roth, M.
2011-06-20
Measurements from tracers and local helioseismology indicate the existence of a meridional flow in the Sun with strength in the order of 15 m s{sup -1} near the solar surface. Different attempts were made to obtain information on the flow profile at depths up to 20 Mm below the solar surface. We propose a method using global helioseismic Doppler measurements with the prospect of inferring the meridional flow profile at greater depths. Our approach is based on the perturbation of the p-mode eigenfunctions of a solar model due to the presence of a flow. The distortion of the oscillation eigenfunctions is manifested in the mixing of p-modes, which may be measured from global solar oscillation time series. As a new helioseismic measurement quantity, we propose amplitude ratios between oscillations in the Fourier domain. We relate this quantity to the meridional flow and unify the concepts presented here for an inversion procedure to infer the meridional flow from global solar oscillations.
Sequential approach to joint flow-seismic inversion for improved characterization of fractured media
NASA Astrophysics Data System (ADS)
Kang, Peter K.; Zheng, Yingcai; Fang, Xinding; Wojcik, Rafal; McLaughlin, Dennis; Brown, Stephen; Fehler, Michael C.; Burns, Daniel R.; Juanes, Ruben
2016-02-01
Seismic interpretation of subsurface structures is traditionally performed without any account of flow behavior. Here we present a methodology for characterizing fractured geologic reservoirs by integrating flow and seismic data. The key element of the proposed approach is the identification—within the inversion—of the intimate relation between fracture compliance and fracture transmissivity, which determine the acoustic and flow responses of a fractured reservoir, respectively. Owing to the strong (but highly uncertain) dependence of fracture transmissivity on fracture compliance, the modeled flow response in a fractured reservoir is highly sensitive to the geophysical interpretation. By means of synthetic models, we show that by incorporating flow data (well pressures and tracer breakthrough curves) into the inversion workflow, we can simultaneously reduce the error in the seismic interpretation and improve predictions of the reservoir flow dynamics. While the inversion results are robust with respect to noise in the data for this synthetic example, the applicability of the methodology remains to be tested for more complex synthetic models and field cases.
A new approach to wall modeling in LES of incompressible flow via function enrichment
NASA Astrophysics Data System (ADS)
Krank, Benjamin; Wall, Wolfgang A.
2016-07-01
A novel approach to wall modeling for the incompressible Navier-Stokes equations including flows of moderate and large Reynolds numbers is presented. The basic idea is that a problem-tailored function space allows prediction of turbulent boundary layer gradients with very coarse meshes. The proposed function space consists of a standard polynomial function space plus an enrichment, which is constructed using Spalding's law-of-the-wall. The enrichment function is not enforced but "allowed" in a consistent way and the overall methodology is much more general and also enables other enrichment functions. The proposed method is closely related to detached-eddy simulation as near-wall turbulence is modeled statistically and large eddies are resolved in the bulk flow. Interpreted in terms of a three-scale separation within the variational multiscale method, the standard scale resolves large eddies and the enrichment scale represents boundary layer turbulence in an averaged sense. The potential of the scheme is shown applying it to turbulent channel flow of friction Reynolds numbers from Reτ = 590 and up to 5,000, flow over periodic constrictions at the Reynolds numbers ReH = 10 , 595 and 19,000 as well as backward-facing step flow at Reh = 5 , 000, all with extremely coarse meshes. Excellent agreement with experimental and DNS data is observed with the first grid point located at up to y1+ = 500 and especially under adverse pressure gradients as well as in separated flows.
The Hawaiian Volcano Observatory's current approach to forecasting lava flow hazards (Invited)
NASA Astrophysics Data System (ADS)
Kauahikaua, J. P.
2013-12-01
Hawaiian Volcanoes are best known for their frequent basaltic eruptions, which typically start with fast-moving channelized `a`a flows fed by high eruptions rates. If the flows continue, they generally transition into pahoehoe flows, fed by lower eruption rates, after a few days to weeks. Kilauea Volcano's ongoing eruption illustrates this--since 1986, effusion at Kilauea has mostly produced pahoehoe. The current state of lava flow simulation is quite advanced, but the simplicity of the models mean that they are most appropriately used during the first, most vigorous, days to weeks of an eruption - during the effusion of `a`a flows. Colleagues at INGV in Catania have shown decisively that MAGFLOW simulations utilizing satellite-derived eruption rates can be effective at estimating hazards during the initial periods of an eruption crisis. However, the algorithms do not simulate the complexity of pahoehoe flows. Forecasts of lava flow hazards are the most common form of volcanic hazard assessments made in Hawai`i. Communications with emergency managers over the last decade have relied on simple steepest-descent line maps, coupled with empirical lava flow advance rate information, to portray the imminence of lava flow hazard to nearby communities. Lavasheds, calculated as watersheds, are used as a broader context for the future flow paths and to advise on the utility of diversion efforts, should they be contemplated. The key is to communicate the uncertainty of any approach used to formulate a forecast and, if the forecast uses simple tools, these communications can be fairly straightforward. The calculation of steepest-descent paths and lavasheds relies on the accuracy of the digital elevation model (DEM) used, so the choice of DEM is critical. In Hawai`i, the best choice is not the most recent but is a 1980s-vintage 10-m DEM--more recent LIDAR and satellite radar DEM are referenced to the ellipsoid and include vegetation effects. On low-slope terrain, steepest
Some Approaches to Modeling Diffuse Flow at Mid-Ocean Ridges
NASA Astrophysics Data System (ADS)
Farough, A.; Lowell, R. P.; Craft, K.; Germanovich, L. N.
2011-12-01
To obtain a sound understanding of subsurface temperatures and the extent of the subsurface biosphere in young oceanic crust, one must understand the mechanisms of diffuse flow at oceanic spreading centers. Mathematical modeling of diffuse flow at oceanic spreading centers has received relatively little attention compared to high-temperature black smoker discharge, in part because the temperature and fluid flow data required to constrain the models are scarce. We review a number of different approaches to modelling diffuse flow: (1) The simplest method considers 1-D steady-state uniform upflow from below subject to a heat transfer boundary condition at the surface, which represents the effects of mixing of hydrothermal fluid with seawater. These models, in which the heat transfer coefficient and the velocity of the ascending fluid are constrained by observed diffuse flow vent temperature and heat flux, typically result in a steep temperature gradient near the seafloor and subsurface biological activity may be limited to the upper few cm of the crust. (2) A related method uses data on the partitioning of heat flux between focused and diffuse flow and chemical data from the focused and diffuse flow components in a two-limb single pass modeling approach to determine the fraction of high-temperature fluid that is incorporated in the diffuse flow. Using data available from EPR 950', the Main Endeavour Field, and ASHES vent field at Axial Volcano on the Juan de Fuca Ridge in conjunction with Mg as a passive tracer, we find that the mixing ratio of high temperature in diffuse flow is <10%. The high-temperature contribution to the diffuse heat flux remains large, however, and high-temperature vent fluid ultimately contributes ~ 90% of the total heat output from the vent field. In these models mixing between high-temperature fluid and seawater may occur over a considerable depth, and the subsurface biosphere may be ~ 100 m deep beneath diffuse flow sites. (3) Finally, in
Spear, Timothy T; Nishimura, Michael I; Simms, Patricia E
2017-08-01
Advancement in flow cytometry reagents and instrumentation has allowed for simultaneous analysis of large numbers of lineage/functional immune cell markers. Highly complex datasets generated by polychromatic flow cytometry require proper analytical software to answer investigators' questions. A problem among many investigators and flow cytometry Shared Resource Laboratories (SRLs), including our own, is a lack of access to a flow cytometry-knowledgeable bioinformatics team, making it difficult to learn and choose appropriate analysis tool(s). Here, we comparatively assess various multidimensional flow cytometry software packages for their ability to answer a specific biologic question and provide graphical representation output suitable for publication, as well as their ease of use and cost. We assessed polyfunctional potential of TCR-transduced T cells, serving as a model evaluation, using multidimensional flow cytometry to analyze 6 intracellular cytokines and degranulation on a per-cell basis. Analysis of 7 parameters resulted in 128 possible combinations of positivity/negativity, far too complex for basic flow cytometry software to analyze fully. Various software packages were used, analysis methods used in each described, and representative output displayed. Of the tools investigated, automated classification of cellular expression by nonlinear stochastic embedding (ACCENSE) and coupled analysis in Pestle/simplified presentation of incredibly complex evaluations (SPICE) provided the most user-friendly manipulations and readable output, evaluating effects of altered antigen-specific stimulation on T cell polyfunctionality. This detailed approach may serve as a model for other investigators/SRLs in selecting the most appropriate software to analyze complex flow cytometry datasets. Further development and awareness of available tools will help guide proper data analysis to answer difficult biologic questions arising from incredibly complex datasets. © Society
Navier-Stokes simulation of transonic wing flow fields using a zonal grid approach
NASA Technical Reports Server (NTRS)
Chaderjian, Neal M.
1988-01-01
The transonic Navier-Stokes code was used to simulate flow fields about isolated wings for workshop wind-tunnel and free-air cases using the thin-layer Reynolds-averaged Navier-Stokes equations. An implicit finite-difference scheme based on a diagonal version of the Beam-Warming algorithm was used to integrate the governing equations. A zonal grid approach was used to allow efficient grid refinement near the wing surface. The flow field was sensitive to the turbulent transition model, and flow unsteadiness was observed for a wind-tunnel case but not for the corresponding free-air case. The specification of experimental pressure at the wind-tunnel exit plane is the primary reason for the difference of these two numerical solutions.
Cyanosis after Kawashima-Fontan: hybrid approach to mixing and matching flows.
Latson, Larry A; Mumtaz, Muhammad A
2011-10-01
Surgical approaches to a single ventricle with absent infrahepatic segment of the inferior vena cava include a bidirectional Glenn and separate hepatic venous connection to the pulmonary arteries. If sites of insertion into the pulmonary arteries are widely separated, hepatic flow is directed to only one lung. Pulmonary arteriovenous malformations may form in the contralateral lung and result in severe cyanosis. We report a case of resolution of pulmonary arteriovenous malformations after successful rerouting of hepatic venous flow to the hemi-azygous vein in a 16-year-old patient. A dilatable pulmonary artery band reduced cyanosis by limiting flow to the affected lung until resolution of pulmonary arteriovenous malformations. Copyright © 2011 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.
The moving boundary approach to modeling gravity-driven stable and unstable flow in soils
NASA Astrophysics Data System (ADS)
Brindt, Naaran; Wallach, Rony
2016-04-01
Many field and laboratory studies in the last 40 years have found that water flow in homogeneous soil profiles may occur in preferential flow pathways rather than in a laterally uniform wetting front, as expected from classical soil physics theory and expressed by the Richards equation. The water-content distribution within such gravity-driven fingers was found to be nonmonotonic due to water accumulation behind a sharp wetting front (denoted as saturation overshoot). The unstable flow was first related to soil coarseness. However, its appearance in water-repellent soils led the authors to hypothesize that gravity-driven unstable flow formation is triggered by a non-zero contact angle between water and soil particles. Despite its widespread occurrence, a macroscopic-type model describing the nonmonotonic water distribution and sharp wetting front is still lacking. The moving boundary approach, which divides the flow domain into two well-defined subdomains with a sharp change in fluid saturation between them, is suggested to replace the classical approach of solving the Richards equation for the entire flow domain. The upper subdomain consists of water and air, whose relationship varies with space and time following the imposed boundary condition at the soil surface as calculated by the Richards equation. The lower subdomain also consists of water and air, but their relationship remains constant following the predetermined initial condition. The moving boundary between the two subdomains is the sharp wetting front, whose location is part of the solution. As such, the problem is inherently nonlinear. The wetting front's movement is controlled by the dynamic water-entry pressure of the soil, which depends on soil wettability and the front's propagation rate. A lower soil wettability, which hinders the spontaneous invasion of dry pores and increases the water-entry pressure, induces a sharp wetting front and water accumulation behind it. The wetting front starts to
A scalable approach to modeling groundwater flow on massively parallel computers
Ashby, S.F.; Falgout, R.D.; Tompson, A.F.B.
1995-12-01
We describe a fully scalable approach to the simulation of groundwater flow on a hierarchy of computing platforms, ranging from workstations to massively parallel computers. Specifically, we advocate the use of scalable conceptual models in which the subsurface model is defined independently of the computational grid on which the simulation takes place. We also describe a scalable multigrid algorithm for computing the groundwater flow velocities. We axe thus able to leverage both the engineer`s time spent developing the conceptual model and the computing resources used in the numerical simulation. We have successfully employed this approach at the LLNL site, where we have run simulations ranging in size from just a few thousand spatial zones (on workstations) to more than eight million spatial zones (on the CRAY T3D)-all using the same conceptual model.
A new lumped-parameter approach to simulating flow processes in unsaturated dual-porosity media
Zimmerman, R.W.; Hadgu, T.; Bodvarsson, G.S.
1995-03-01
We have developed a new lumped-parameter dual-porosity approach to simulating unsaturated flow processes in fractured rocks. Fluid flow between the fracture network and the matrix blocks is described by a nonlinear equation that relates the imbibition rate to the local difference in liquid-phase pressure between the fractures and the matrix blocks. This equation is a generalization of the Warren-Root equation, but unlike the Warren-Root equation, is accurate in both the early and late time regimes. The fracture/matrix interflow equation has been incorporated into a computational module, compatible with the TOUGH simulator, to serve as a source/sink term for fracture elements. The new approach achieves accuracy comparable to simulations in which the matrix blocks are discretized, but typically requires an order of magnitude less computational time.
An approach for drag correction based on the local heterogeneity for gas-solid flows
Li, Tingwen; Wang, Limin; Rogers, William; Zhou, Guofeng; Ge, Wei
2016-09-22
The drag models typically used for gas-solids interaction are mainly developed based on homogeneous systems of flow passing fixed particle assembly. It has been shown that the heterogeneous structures, i.e., clusters and bubbles in fluidized beds, need to be resolved to account for their effect in the numerical simulations. Since the heterogeneity is essentially captured through the local concentration gradient in the computational cells, this study proposes a simple approach to account for the non-uniformity of solids spatial distribution inside a computational cell and its effect on the interaction between gas and solid phases. Finally, to validate this approach, the predicted drag coefficient has been compared to the results from direct numerical simulations. In addition, the need to account for this type of heterogeneity is discussed for a periodic riser flow simulation with highly resolved numerical grids and the impact of the proposed correction for drag is demonstrated.
An approach for drag correction based on the local heterogeneity for gas-solid flows
Li, Tingwen; Wang, Limin; Rogers, William; ...
2016-09-22
The drag models typically used for gas-solids interaction are mainly developed based on homogeneous systems of flow passing fixed particle assembly. It has been shown that the heterogeneous structures, i.e., clusters and bubbles in fluidized beds, need to be resolved to account for their effect in the numerical simulations. Since the heterogeneity is essentially captured through the local concentration gradient in the computational cells, this study proposes a simple approach to account for the non-uniformity of solids spatial distribution inside a computational cell and its effect on the interaction between gas and solid phases. Finally, to validate this approach, themore » predicted drag coefficient has been compared to the results from direct numerical simulations. In addition, the need to account for this type of heterogeneity is discussed for a periodic riser flow simulation with highly resolved numerical grids and the impact of the proposed correction for drag is demonstrated.« less
A triple-continuum approach for modeling flow and transport processes in fractured rock.
Wu, Yu-Shu; Liu, H H; Bodvarsson, G S
2004-09-01
This paper presents a triple-continuum conceptual model for simulating flow and transport processes in fractured rock. Field data collected from the unsaturated zone of Yucca Mountain, a repository site of high-level nuclear waste, show a large number of small-scale fractures. The effect of these small fractures has not been considered in previous modeling investigations within the context of a continuum approach. A new triple-continuum model (consisting of matrix, small-fracture, and large-fracture continua) has been developed to investigate the effect of these small fractures. This paper derives the model formulation and discusses the basic triple-continuum behavior of flow and transport processes under different conditions, using both analytical solutions and numerical approaches. The simulation results from the site-scale model of the unsaturated zone of Yucca Mountain indicate that these small fractures may have an important effect on radionuclide transport within the mountain. Copyright 2004 Elsevier B.V.
A simplified approach for the computation of steady two-phase flow in inverted siphons.
Diogo, A Freire; Oliveira, Maria C
2016-01-15
Hydraulic, sanitary, and sulfide control conditions of inverted siphons, particularly in large wastewater systems, can be substantially improved by continuous air injection in the base of the inclined rising branch. This paper presents a simplified approach that was developed for the two-phase flow of the rising branch using the energy equation for a steady pipe flow, based on the average fluid fraction, observed slippage between phases, and isothermal assumption. As in a conventional siphon design, open channel steady uniform flow is assumed in inlet and outlet chambers, corresponding to the wastewater hydraulic characteristics in the upstream and downstream sewers, and the descending branch operates in steady uniform single-phase pipe flow. The proposed approach is tested and compared with data obtained in an experimental siphon setup with two plastic barrels of different diameters operating separately as in a single-barrel siphon. Although the formulations developed are very simple, the results show a good adjustment for the set of the parameters used and conditions tested and are promising mainly for sanitary siphons with relatively moderate heights of the ascending branch.
Evaluating the spore genome sizes of ferns and lycophytes: a flow cytometry approach.
Kuo, Li-Yaung; Huang, Yi-Jia; Chang, JenYu; Chiou, Wen-Liang; Huang, Yao-Moan
2017-03-01
Ferns and lycophytes produce spores to initiate the gametophyte stage for sexual reproduction. Approximately 10% of these seedless vascular plants are apomictic, and produce genomic unreduced spores. Genome size comparisons between spores and leaves are a reliable, and potentially easier way to determine their reproductive mode compared to traditional approaches. However, estimation of the spore genome sizes of these plants has not been attempted. We attempted to evaluate the spore genome sizes of ferns and lycophytes using flow cytometry, collected spores from selected species representing different spore physical properties and taxonomic groups, and sought to optimize bead-vortexing conditions. By evaluating the spore and sporophyte genome sizes, we examined whether reproductive modes could be ascertained from these flow cytometry results. We proposed two separate sets of optimized bead-vortexing conditions for the nuclear extraction of green and nongreen spores. We further successfully extracted spore nuclei of 19 families covering most orders, and the qualities and quantities of these extractions satisfied the C-value criteria. These evaluated genome sizes further supported the reproductive modes reported previously. In the current study, flow cytometry was used for the first time to evaluate the spore genome sizes of ferns and lycophytes. This use of spore flow cytometry provides a new, efficient approach to ascertaining the reproductive modes of these plants.
The sandwich estimator approach counting for inter-site dependence of extreme river flow in Sabah
NASA Astrophysics Data System (ADS)
Kahal Musakkal, N. F.; Gabda, D.
2017-09-01
Regional estimation method is often used for estimating parameters of a distribution when data are available at many sites in a region to capture inter-site dependence. In this paper, we fit generalized extreme value distribution independently to model data of river flows at each sites in Sabah to avoid extreme value complex modeling. Since our approach violated the condition of spatial analysis, we consider the adjusted standard error to correct the wrong assumption of our marginal approach. As a result, we have an appropriate corrected variance of the generalized extreme value parameters.
A new approach to high-speed flow measurements using constant voltage anemometry
NASA Technical Reports Server (NTRS)
Mangalam, S. M.; Sarma, G. R.; Kuppa, S.; Kubendran, L. R.
1992-01-01
The paper addresses the basic features of conventional instrumentation, such as the constant temperature (CTA) and the constant current (CCA) anemometers, their limitations, and describes a totally new approach to high-speed dynamic measurements using a constant voltage anemometer (CVA). The paper describes the design features of a newly developed CVA and compares preliminary results obtained with CVA and conventional anemometry in low- and high-speed flows.
Advanced digital methods for blood flow flux analysis using µPIV approach
NASA Astrophysics Data System (ADS)
Kurochkin, Maxim A.; Timoshina, Polina A.; Fedosov, Ivan V.; Tuchin, Valery V.
2015-03-01
A digital optical system focused on work with laboratory animals for intravital capillaroscopy has been developed. It implements the particle image velocimetry (PIV) based approach for measurements of red blood cells velocity in laboratory rat stomach capillaries. We propose a method of involuntary displacement compensation of the capillary network images. Image stabilization algorithm is based on correlation of feature tracking. The efficiency of designed image stabilization algorithm was experimentally demonstrated. The results of capillary blood flow analysis are demonstrated.
A new approach in cascade flow analysis using the finite element method
NASA Technical Reports Server (NTRS)
Baskharone, E.; Hamed, A.
1980-01-01
A new approach in analyzing the potential flow past cascades and single airfoils using the finite element method is developed. In this analysis the circulation around the airfoil is not externally imposed but is directly computed in the numerical solution. Different finite element discretization patterns, orders of piecewise approximation, and grid sizes are used in the solution. The results obtained are compared with existing experimental measurements and exact solutions in cascades and single airfoils.
A new approach to high-speed flow measurements using constant voltage anemometry
NASA Technical Reports Server (NTRS)
Mangalam, S. M.; Sarma, G. R.; Kuppa, S.; Kubendran, L. R.
1992-01-01
The paper addresses the basic features of conventional instrumentation, such as the constant temperature (CTA) and the constant current (CCA) anemometers, their limitations, and describes a totally new approach to high-speed dynamic measurements using a constant voltage anemometer (CVA). The paper describes the design features of a newly developed CVA and compares preliminary results obtained with CVA and conventional anemometry in low- and high-speed flows.
A genetic algorithm-based approach to flexible flow-line scheduling with variable lot sizes.
Lee, I; Sikora, R; Shaw, M J
1997-01-01
Genetic algorithms (GAs) have been used widely for such combinatorial optimization problems as the traveling salesman problem (TSP), the quadratic assignment problem (QAP), and job shop scheduling. In all of these problems there is usually a well defined representation which GA's use to solve the problem. We present a novel approach for solving two related problems-lot sizing and sequencing-concurrently using GAs. The essence of our approach lies in the concept of using a unified representation for the information about both the lot sizes and the sequence and enabling GAs to evolve the chromosome by replacing primitive genes with good building blocks. In addition, a simulated annealing procedure is incorporated to further improve the performance. We evaluate the performance of applying the above approach to flexible flow line scheduling with variable lot sizes for an actual manufacturing facility, comparing it to such alternative approaches as pair wise exchange improvement, tabu search, and simulated annealing procedures. The results show the efficacy of this approach for flexible flow line scheduling.
A network theory approach for a better understanding of overland flow connectivity
NASA Astrophysics Data System (ADS)
Masselink, Rens; Heckmann, Tobias; Temme, Arnaud; Anders, Niels; Keesstra, Saskia
2016-04-01
Hydrological connectivity describes the physical coupling, or linkages of different elements within a landscape regarding (sub)surface flows. A firm understanding of hydrological connectivity is important for catchment management applications, for e.g. habitat and species protection, and for flood resistance and resilience improvement. Thinking about (geomorphological) systems as networks can lead to new insights, which has been recognised within the scientific community as well, seeing the recent increase in the use of network (graph) theory within the geosciences. Network theory supports the analysis and understanding of complex systems by providing data structures for modelling objects and their linkages, and a versatile toolbox to quantitatively appraise network structure and properties. The objective of this study was to characterise overland flow connectivity dynamics on hillslopes in a humid sub-Mediterranean environment by using a combination of high-resolution digital-terrain models, overland flow sensors and a network approach. Results showed that there are significant differences between overland flow on agricultural areas and semi-natural shrubs areas. Positive correlations between connectivity and precipitation characteristics were found, while negative correlations between connectivity and soil moisture were found, probably due to soil water repellency. The combination of a structural network to determine potential connectivity with dynamic networks to determine the actual connectivity proved a powerful tool in analysing overland flow connectivity.
A computational approach to modeling cellular-scale blood flow in complex geometry
NASA Astrophysics Data System (ADS)
Balogh, Peter; Bagchi, Prosenjit
2017-04-01
We present a computational methodology for modeling cellular-scale blood flow in arbitrary and highly complex geometry. Our approach is based on immersed-boundary methods, which allow modeling flows in arbitrary geometry while resolving the large deformation and dynamics of every blood cell with high fidelity. The present methodology seamlessly integrates different modeling components dealing with stationary rigid boundaries of complex shape, moving rigid bodies, and highly deformable interfaces governed by nonlinear elasticity. Thus it enables us to simulate 'whole' blood suspensions flowing through physiologically realistic microvascular networks that are characterized by multiple bifurcating and merging vessels, as well as geometrically complex lab-on-chip devices. The focus of the present work is on the development of a versatile numerical technique that is able to consider deformable cells and rigid bodies flowing in three-dimensional arbitrarily complex geometries over a diverse range of scenarios. After describing the methodology, a series of validation studies are presented against analytical theory, experimental data, and previous numerical results. Then, the capability of the methodology is demonstrated by simulating flows of deformable blood cells and heterogeneous cell suspensions in both physiologically realistic microvascular networks and geometrically intricate microfluidic devices. It is shown that the methodology can predict several complex microhemodynamic phenomena observed in vascular networks and microfluidic devices. The present methodology is robust and versatile, and has the potential to scale up to very large microvascular networks at organ levels.
NASA Technical Reports Server (NTRS)
Goldstein, David B.; Varghese, Philip L.
1997-01-01
We proposed to create a single computational code incorporating methods that can model both rarefied and continuum flow to enable the efficient simulation of flow about space craft and high altitude hypersonic aerospace vehicles. The code was to use a single grid structure that permits a smooth transition between the continuum and rarefied portions of the flow. Developing an appropriate computational boundary between the two regions represented a major challenge. The primary approach chosen involves coupling a four-speed Lattice Boltzmann model for the continuum flow with the DSMC method in the rarefied regime. We also explored the possibility of using a standard finite difference Navier Stokes solver for the continuum flow. With the resulting code we will ultimately investigate three-dimensional plume impingement effects, a subject of critical importance to NASA and related to the work of Drs. Forrest Lumpkin, Steve Fitzgerald and Jay Le Beau at Johnson Space Center. Below is a brief background on the project and a summary of the results as of the end of the grant.
Two-phase flow in complex geometries: A diffuse domain approach
Aland, S.; Voigt, A.
2011-01-01
We present a new method for simulating two-phase flows in complex geometries, taking into account contact lines separating immiscible incompressible components. We combine the diffuse domain method for solving PDEs in complex geometries with the diffuse-interface (phase-field) method for simulating multiphase flows. In this approach, the complex geometry is described implicitly by introducing a new phase-field variable, which is a smooth approximation of the characteristic function of the complex domain. The fluid and component concentration equations are reformulated and solved in larger regular domain with the boundary conditions being implicitly modeled using source terms. The method is straightforward to implement using standard software packages; we use adaptive finite elements here. We present numerical examples demonstrating the effectiveness of the algorithm. We simulate multiphase flow in a driven cavity on an extended domain and find very good agreement with results obtained by solving the equations and boundary conditions in the original domain. We then consider successively more complex geometries and simulate a droplet sliding down a rippled ramp in 2D and 3D, a droplet flowing through a Y-junction in a microfluidic network and finally chaotic mixing in a droplet flowing through a winding, serpentine channel. The latter example actually incorporates two different diffuse domains: one describes the evolving droplet where mixing occurs while the other describes the channel. PMID:21918638
Study of downward annular pipe flow using combined laser-based approaches
NASA Astrophysics Data System (ADS)
An, Jae Sik; Cherdantsev, Andrey; Zadrazil, Ivan; Matar, Omar; Markides, Christos
2016-11-01
In downward annular flow, the liquid phase flows as a film along the pipe wall and the gas flows in the core of the pipe. The liquid free-surface is covered by a complex multiscale system of waves. The interaction dynamics of the interfacial waves with each other and with the gas stream exert a significant influence on the pressure drop, heat transfer and mass interchange between the phases. The complexity of the interface requires the application of measurement techniques with high spatiotemporal resolution. In this work, two approaches based on the principle of laser-induced fluorescence, namely planar LIF and brightness-based LIF, are applied simultaneously to study interfacial phenomena in these flows, while simultaneous LIF and PIV are used to obtain velocity field information in the liquid phase underneath the waves. Sources of measurement bias are then analysed: total internal reflection at the out-of-plane interface; steep longitudinal slopes and transverse wave curvature; presence of gas bubbles in the liquid film. Although each method has its own limitations, a combined technique can provide reliable spatiotemporal measurements of film thickness to accompany the velocity information. Finally, flow development is studied in a moving frame of reference over long lengths. EPSRC UK Programme Grant MEMPHIS (EP/K003976/1).
A Dual Model-Reduction Approach to Groundwater Flow and Solute Transport Simulations.
NASA Astrophysics Data System (ADS)
Stanko, Z.; Boyce, S. E.; Yeh, W. W. G.
2014-12-01
Mathematical-model reduction using singular value decomposition (SVD) has been shown to be an effective method for reducing the computer runtime of linear and nonlinear groundwater-flow models without sacrificing accuracy. The discrete empirical interpolation method (DEIM) is an alternate method of model reduction better suited for nonlinear systems. In this research, both methods are applied simultaneously to reduce the dimensionality of a 3-D unconfined groundwater-flow model: SVD to reduce the column space and DEIM to reduce the row space. The results of the dimensional reduction can approach several orders of magnitude, resulting in significantly faster simulation runtimes. The implementation and benefit of SVD/DEIM model reduction is demonstrated through its application to a synthetic, groundwater-flow and solute-transport model with groundwater extraction wells that influence of seawater intrusion. The developed methodology identifies the dominant locations (i.e. the discrete points) of the model that have the most influence on the water levels and saltwater concentrations. The result is a reduced model constructed from fewer equations (row dimension) and is projected into a reduced subspace (column dimension). The methodology first independently constructs the reduced flow and transport models such that their errors are minimized for a flow-only model and transport-only model, respectively. Once the two reduced models have been established, a density-dependent flow simulation is preformed by iterating between the flow and transport models for each time step. Further analysis of the SVD/DEIM method illustrates the tradeoff between magnitude of the reduced dimension and corresponding errors in model output, with respect to the unreduced and independently reduced models. The application of this method shows that runtime can be significantly decreased for models of this type while still maintaining control of desired model accuracy.
Delay, Frederick; Porel, Gilles; Chatelier, Marion
2013-07-01
We present a modeling exercise of solute transport and biodegradation in a coarse porous medium widely colonized by a biofilm phase. Tracer tests in large laboratory columns using both conservative (fluorescein) and biodegradable (nitrate) solutes are simulated by means of a dual flowing continuum approach. The latter clearly distinguishes concentrations in a flowing porous phase from concentrations conveyed in the biofilm. With this conceptual setting, it becomes possible to simulate the sharp front of concentrations at early times and the flat tail of low concentrations at late times observed on the experimental breakthrough curves. Thanks to the separation of flow in two phases at different velocities, dispersion coefficients in both flowing phases keep reasonable values with some physical meaning. This is not the case with simpler models based on a single continuum (eventually concealing dead-ends), for which inferred dispersivity may reach the unphysical value of twice the size of the columns. We also show that the behavior of the dual flowing continuum is mainly controlled by the relative fractions of flow passing in each phase and the rate of mass transfer between phases. These parameters also condition the efficiency of nitrate degradation, the degradation rate in a well-seeded medium being a weakly sensitive parameter. Even though the concept of dual flowing continuum appears promising for simulating transport in complex porous media, its inversion onto experimental data really benefits from attempts with simpler models providing a rough pre-evaluation of parameters such as porosity and mean fluid velocity in the system. Copyright © 2013 Elsevier B.V. All rights reserved.
NASA Astrophysics Data System (ADS)
Chang, Ching-Min; Yeh, Hund-Der
2009-01-01
This paper describes a stochastic analysis of steady state flow in a bounded, partially saturated heterogeneous porous medium subject to distributed infiltration. The presence of boundary conditions leads to non-uniformity in the mean unsaturated flow, which in turn causes non-stationarity in the statistics of velocity fields. Motivated by this, our aim is to investigate the impact of boundary conditions on the behavior of field-scale unsaturated flow. Within the framework of spectral theory based on Fourier-Stieltjes representations for the perturbed quantities, the general expressions for the pressure head variance, variance of log unsaturated hydraulic conductivity and variance of the specific discharge are presented in the wave number domain. Closed-form expressions are developed for the simplified case of statistical isotropy of the log hydraulic conductivity field with a constant soil pore-size distribution parameter. These expressions allow us to investigate the impact of the boundary conditions, namely the vertical infiltration from the soil surface and a prescribed pressure head at a certain depth below the soil surface. It is found that the boundary conditions are critical in predicting uncertainty in bounded unsaturated flow. Our analytical expression for the pressure head variance in a one-dimensional, heterogeneous flow domain, developed using a nonstationary spectral representation approach [Li S-G, McLaughlin D. A nonstationary spectral method for solving stochastic groundwater problems: unconditional analysis. Water Resour Res 1991;27(7):1589-605; Li S-G, McLaughlin D. Using the nonstationary spectral method to analyze flow through heterogeneous trending media. Water Resour Res 1995; 31(3):541-51], is precisely equivalent to the published result of Lu et al. [Lu Z, Zhang D. Analytical solutions to steady state unsaturated flow in layered, randomly heterogeneous soils via Kirchhoff transformation. Adv Water Resour 2004;27:775-84].
Astrium Approach For Plume Flow And Impingement Of 10 N Bipropellant Thruster
NASA Astrophysics Data System (ADS)
Theroude, Christophe; Scremin, G.; Wartelski, Matias
2011-05-01
Plume impingement on spacecraft surfaces due to chemical propulsion is a major concern during satellite operations. Indeed, thrusters plume induces disturbing forces and torques, contamination as well as thermal fluxes on sensitive surfaces. These effects, that have to be accurately predicted, influence the satellite design: thrusters orientation, MLI design, instruments protections, etc. In order to implement an efficient process of analysis, Astrium uses a two steps approach: first the thruster undisturbed flow field is computed, then the impingement on spacecraft surfaces is evaluated. In this paper, Plumflow, the Astrium Satellites software for undisturbed thrusters’ plume computation, is presented. This software is made of several modules in order to accurately compute the flow field in the different parts of the plume. A first module computes the chemistry in the chamber, then Navier-Stokes equations are solved inside the nozzle where the flow is continuous. After that a DSMC code is used for the transitional regime near the thruster lip and finally an hybrid TPMC/source-flow method computes the free molecular far flow field. The studied case is the Astrium GmbH 10 N bipropellant thruster. Some comparisons are presented between Plumflow and Professor G.A. Bird DSMC software DS2V and with DLR experimental data. These comparisons have shown very satisfactory results. Finally, aiming at computing plume impingement, the plume flow field generated with Plumflow has been interfaced with Professor G.A. Bird 3D DSMC software DS3V. The plume impingement simulation is performed by introducing the undisturbed flow field at a boundary of DS3V computational domain. It allows us to evaluate thermal flux distribution due to Astrium 10 N thruster on a plate adjacent to the thruster and to compare with the Astrium plume impingement software.
The moving-boundary approach for modeling gravity-driven stable and unstable flow in soils
NASA Astrophysics Data System (ADS)
Brindt, Naaran; Wallach, Rony
2017-01-01
The Richards equation is unsuccessful at describing gravity-driven unstable flow with nonmonotonic water content distribution. This shortcoming is resolved in the current study by introducing the moving-boundary approach. Following this approach, the flow domain is divided into two subdomains with a sharp change in fluid saturation between them (moving boundary). The upper subdomain consists of water and air, whose relationship varies with space and time following the imposed boundary condition at the soil surface calculated by the Richards equation. The lower subdomain consists of an initially dry soil that remains constant. The location of the boundary between the two subdomains is part of the solution, rendering the problem nonlinear. The moving boundary solution was used after verification to demonstrate the effect of contact angle, soil characteristic curves and incoming flux on the dynamic water-entry pressure of the soil, which depends on the soil's wettability, incoming flux at the soil surface and the wetting front's propagation rate. Lower soil wettability hinders spontaneous invasion of the dry pores and, together with a higher input flux, induces water accumulation behind the wetting front (saturation overshoot). The wetting front starts to propagate once the pressure building up behind it exceeds the dynamic water-entry pressure. To conclude, the physically based novel moving-boundary approach for solving stable and gravity-driven unstable flow in soils was developed and verified. It supports the conjecture that saturation overshoot is a prerequisite for gravity-driven fingering.
Guo, Hao; Tian, Yimei; Shen, Hailiang; Wang, Yi; Kang, Mengxin
A design approach for determining the optimal flow pattern in a landscape lake is proposed based on FLUENT simulation, multiple objective optimization, and parallel computing. This paper formulates the design into a multi-objective optimization problem, with lake circulation effects and operation cost as two objectives, and solves the optimization problem with non-dominated sorting genetic algorithm II. The lake flow pattern is modelled in FLUENT. The parallelization aims at multiple FLUENT instance runs, which is different from the FLUENT internal parallel solver. This approach: (1) proposes lake flow pattern metrics, i.e. weighted average water flow velocity, water volume percentage of low flow velocity, and variance of flow velocity, (2) defines user defined functions for boundary setting, objective and constraints calculation, and (3) parallels the execution of multiple FLUENT instances runs to significantly reduce the optimization wall-clock time. The proposed approach is demonstrated through a case study for Meijiang Lake in Tianjin, China.
A general approach for modeling the motion of rigid and deformable ellipsoids in ductile flows
NASA Astrophysics Data System (ADS)
Jiang, Dazhi
2012-01-01
A general approach for modeling the motion of rigid or deformable objects in viscous flows is presented. It is shown that the rotation of a 3D object in a viscous fluid, regardless of the mechanical property and shape of the object, is defined by a common and simple differential equation, dQ/dt=-Θ˜Q, where Q is a matrix defined by the orientation of the object and Θ˜ is the angular velocity tensor of the object. The difference between individual cases lies only in the formulation for the angular velocity. Thus the above equation, together with Jeffery's theory for the angular velocity of rigid ellipsoids, describes the motion of rigid ellipsoids in viscous flows. The same equation, together with Eshelby's theory for the angular velocity of deformable ellipsoids, describes the motion of deformable ellipsoids in viscous flows. Both problems are solved here numerically by a general approach that is much simpler conceptually and more economic computationally, compared to previous approaches that consider the problems separately and require numerical solutions to coupled differential equations about Euler angles or spherical (polar coordinate) angles. A Runge-Kutta approximation is constructed for solving the above general differential equation. Singular cases of Eshelby's equations when the object is spheroidal or spherical are handled in this paper in a much simpler way than in previous work. The computational procedure can be readily implemented in any modern mathematics application that handles matrix operations. Four MathCad Worksheets are provided for modeling the motion of a single rigid or deformable ellipsoid immersed in viscous fluids, as well as the evolution of a system of noninteracting rigid or deformable ellipsoids embedded in viscous flows.
Flow adjustment inside large finite-size wind farms approaching the infinite wind farm regime
NASA Astrophysics Data System (ADS)
Wu, Ka Ling; Porté-Agel, Fernando
2017-04-01
Due to the increasing number and the growing size of wind farms, the distance among them continues to decrease. Thus, it is necessary to understand how these large finite-size wind farms and their wakes could interfere the atmospheric boundary layer (ABL) dynamics and adjacent wind farms. Fully-developed flow inside wind farms has been extensively studied through numerical simulations of infinite wind farms. The transportation of momentum and energy is only vertical and the advection of them is neglected in these infinite wind farms. However, less attention has been paid to examine the length of wind farms required to reach such asymptotic regime and the ABL dynamics in the leading and trailing edges of the large finite-size wind farms. Large eddy simulations are performed in this study to investigate the flow adjustment inside large finite-size wind farms in conventionally-neutral boundary layer with the effect of Coriolis force and free-atmosphere stratification from 1 to 5 K/km. For the large finite-size wind farms considered in the present work, when the potential temperature lapse rate is 5 K/km, the wind farms exceed the height of the ABL by two orders of magnitude for the incoming flow inside the farms to approach the fully-developed regime. An entrance fetch of approximately 40 times of the ABL height is also required for such flow adjustment. At the fully-developed flow regime of the large finite-size wind farms, the flow characteristics match those of infinite wind farms even though they have different adjustment length scales. The role of advection at the entrance and exit regions of the large finite-size wind farms is also examined. The interaction between the internal boundary layer developed above the large finite-size wind farms and the ABL under different potential temperature lapse rates are compared. It is shown that the potential temperature lapse rate plays a role in whether the flow inside the large finite-size wind farms adjusts to the fully
Different approaches to assess the volume of debris-flows deposits: are results comparable?
NASA Astrophysics Data System (ADS)
Michelini, T.; Bertoldi, G.; D'Agostino, V.
2012-04-01
Debris-flow hazard planning is heavily dependent on the sediment-volume estimation along with its expected frequency. The reliable determination of this variable allows debris-flow simulation and derives from several methods: statistical elaboration of maximum rainfall/runoff/sediment volumes series, empirical approaches based on catchment morphology, and field surveys on the potential sediment availability. The historical series analysis should be one of the best solution to assess debris-flow magnitude and frequency, especially for unlimited sediment supply basins. Nevertheless this task is difficult due to the lack or non homogeneity of data. Over last decades some Alpine catchments authorities have initiated to systematically record the event features by means of post-event measures, but there is not yet a definitive standard method. An analysis on the variable estimation of volumes of debris-flow deposits volume is here presented. Study area is located in Italian Central Alps and deals with three neighboring small catchments (<5 square kilometers) characterized by unaltered and almost natural fans at the left side of the Sarca river of 'Val Genova' (Trentino Region, Italy). The investigated catchments, Dosson, Cercen and Gabbiolo, have an unlimited sediment supply which causes granular debris flows made of granitic cobbles and boulders in a sandy matrix. Five recent debris flows events have been studied: two occurred on the 11th of July 2010 and on the 20th of September 1999 in the Dosson torrent, one occurred on the 24th-25th of August 1987 in the Cercen torrent, and two on the 25th of September 2006 and on the 20th of September 1999 in the Gabbiolo torrent. The integration of digital terrain model analysis, information about soil geomorphology and forestry cover, and field observations has allowed mapping the debris-flow deposits. Furthermore, data about deposit thicknesses and angles of deposition at the fan surface were measured. Thanks to these data some
A Hybrid Continuum / Particle Approach for Micro-Scale Gas Flows
NASA Astrophysics Data System (ADS)
Sun, Quanhua; Boyd, Iain D.; Candler, Graham V.
2003-05-01
A hybrid continuum/particle approach is proposed for micro scale gas flows in this paper. The approach couples the DSMC-IP method and a Navier-Stokes solver with an adaptive interface. The continuum solver uses the particle cells as ghost cells because the IP method preserves the hydrodynamic information that the continuum solver uses. In order to generate particles from the continuum side, two strategies are proposed. The first one uses a condition similar to the Marshak condition in generating particles through the interface. The second strategy adopts buffer cells and reservoir cells, which avoids directly generating particles. The interface is determined by a continuum breakdown parameter that is evaluated in every time step. In order to track the interface, a mapping technique is used in the code. Numerical examples show that the hybrid approach couples the continuum solver and the particle method very smoothly. Simulated results also show the effects of the cutoff value of the continuum breakdown parameter.
A velocity tracking approach for the data assimilation problem in blood flow simulations.
Tiago, J; Guerra, T; Sequeira, A
2016-11-24
Several advances have been made in data assimilation techniques applied to blood flow modeling. Typically, idealized boundary conditions, only verified in straight parts of the vessel, are assumed. We present a general approach, on the basis of a Dirichlet boundary control problem, that may potentially be used in different parts of the arterial system. The relevance of this method appears when computational reconstructions of the 3D domains, prone to be considered sufficiently extended, are either not possible, or desirable, because of computational costs. On the basis of taking a fully unknown velocity profile as the control, the approach uses a discretize then optimize methodology to solve the control problem numerically. The methodology is applied to a realistic 3D geometry representing a brain aneurysm. The results show that this data assimilation approach may be preferable to a pressure control strategy and that it can significantly improve the accuracy associated to typical solutions obtained using idealized velocity profiles.
A scenario neutral approach to assess low flow sensitivity to climate change
NASA Astrophysics Data System (ADS)
Sauquet, Eric; Prudhomme, Christel
2015-04-01
Most impact studies of climate change on river flow regime are performed following top-down approaches, where changes in hydrological characteristics are obtained from rainfall-runoff models forced by downscaled projections provided by GCMs. However, such approaches are not always considered robust enough to bridge the gap between climate research and stake holders needs to develop relevant adaptation strategy (Wilby et al., 2014). Alternatively, 'bottom-up' approaches can be applied to climate change impact studies on water resources to assess the intrinsic vulnerability of the catchments and ultimately help to prioritize adaptation actions for areas highly sensitive to small deviations from the present-day climate conditions. A general framework combining the scenario-neutral methodology developed by Prudhomme et al. (2010) and climate elasticity analyses (Sankarasubramanian et al., 2001) is presented and applied to measure the vulnerability of low flows and droughts on a large dataset of more than 400 French gauged basins. The different steps involved in the suggested framework are: - Calibration of the GR5J rainfall runoff model (Pushpalatha et al., 2011) against observations, - Identification of the main climate factors influencing low flows, - Definition of the sensitivity domain for precipitation (P), temperature (T) and potential evapotranspiration (PE) scenarios consistent with most recent climate change projections, - Derivation of the response surface describing changes in low flow and drought regime in terms of severity, duration and seasonality (Catalogne, 2012), - Uncertainty assessment. Results are the basis for a classification of river basins according to their sensitivity at national scale and for discussions on adaptation requirements with stakeholders. Catalogne C (2012) Amélioration des méthodes de prédétermination des débits de référence d'étiage en sites peu ou pas jaugés. PHD thesis, Université Joseph Fourier, Grenoble, 285 pp
An Aerial-Image Dense Matching Approach Based on Optical Flow Field
NASA Astrophysics Data System (ADS)
Yuan, Wei; Chen, Shiyu; Zhang, Yong; Gong, Jianya; Shibasaki, Ryosuke
2016-06-01
Dense matching plays an important role in many fields, such as DEM (digital evaluation model) producing, robot navigation and 3D environment reconstruction. Traditional approaches may meet the demand of accuracy. But the calculation time and out puts density is hardly be accepted. Focus on the matching efficiency and complex terrain surface matching feasibility an aerial image dense matching method based on optical flow field is proposed in this paper. First, some high accurate and uniformed control points are extracted by using the feature based matching method. Then the optical flow is calculated by using these control points, so as to determine the similar region between two images. Second, the optical flow field is interpolated by using the multi-level B-spline interpolation in the similar region and accomplished the pixel by pixel coarse matching. Final, the results related to the coarse matching refinement based on the combined constraint, which recognizes the same points between images. The experimental results have shown that our method can achieve per-pixel dense matching points, the matching accuracy achieves sub-pixel level, and fully meet the three-dimensional reconstruction and automatic generation of DSM-intensive matching's requirements. The comparison experiments demonstrated that our approach's matching efficiency is higher than semi-global matching (SGM) and Patch-based multi-view stereo matching (PMVS) which verifies the feasibility and effectiveness of the algorithm.
Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.
Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert
2009-08-01
This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.
Hydrologic and geochemical approaches for determining ground-water flow components
Hjalmarson, H.W.; Robertson, F.N.
1991-01-01
Lyman Lake is an irrigation-storage reservoir on the Little Colorado River near St. Johns, Arizona. The main sources of water for the lake are streamflow in the Little Colorado River and ground-water inflow from the underlying Coconino aquifer. Two approaches, a hydrologic analysis and a geochemical analysis, were used to compute the quantity of ground-water flow to and from Lyman Lake. Hydrologic data used to calculate a water budget were precipitation on the lake, evaporation from the lake, transpiration from dense vegetation, seepage through the dam, streamflow in and out of the lake, and changes in lake storage. Geochemical data used to calculate the ground-water flow components were major ions, trace elements, and the stable isotopes of hydrogen and oxygen. During the study, the potentiometric level of the Coconino aquifer was above the lake level at the upstream end of the lake and below the lake level at the downstream end. Hydrologic and geochemical data indicate that about 10 percent and 8 percent, respectively, of the water in the lake is ground-water inflow and that about 35 percent of the water in the Little Colorado River 6 miles downgradient from the lake near Salado Springs is ground water. These independent estimates of ground-water flow derived from each approach are in agreement and support a conceptual model of the water budget.
An implicit and adaptive nonlinear frequency domain approach for periodic viscous flows
NASA Astrophysics Data System (ADS)
Mosahebi, A.; Nadarajah, S.
2014-12-01
An implicit nonlinear Lower-Upper symmetric Gauss-Seidel (LU-SGS) solver has been extended to the adaptive Nonlinear Frequency Domain method (adaptive NLFD) for periodic viscous flows. The discretized equations are linearized in both spatial and temporal directions, yielding an innovative segregate approach, where the effects of the neighboring cells are transferred to the right-hand-side and are updated iteratively. This property of the solver is aligned with the adaptive NLFD concept, in which different cells have different number of modes; hence, should be treated individually. The segregate analysis of the modal equations prevents assembling and inversion of a large left-hand-side matrix, when high number of modes are involved. This is an important characteristic for a selected flow solver of the adaptive NLFD method, where a high modal content may be required in highly unsteady parts of the flow field. The implicit nonlinear LU-SGS solver has demonstrated to be both robust and computationally efficient as the number of modes is increased. The developed solver is thoroughly validated for the laminar vortex shedding behind a stationary cylinder, high angle of attack NACA0012 airfoil, and a plunging NACA0012 airfoil. An order of magnitude improvement in the computational time is observed through the developed implicit approach over the classical modified 5-stage Runge-Kutta method.
Review of numerical models of cavitating flows with the use of the homogeneous approach
NASA Astrophysics Data System (ADS)
Niedźwiedzka, Agnieszka; Schnerr, Günter H.; Sobieski, Wojciech
2016-06-01
The focus of research works on cavitation has changed since the 1960s; the behaviour of a single bubble is no more the area of interest for most scientists. Its place was taken by the cavitating flow considered as a whole. Many numerical models of cavitating flows came into being within the space of the last fifty years. They can be divided into two groups: multi-fluid and homogeneous (i.e., single-fluid) models. The group of homogenous models contains two subgroups: models based on transport equation and pressure based models. Several works tried to order particular approaches and presented short reviews of selected studies. However, these classifications are too rough to be treated as sufficiently accurate. The aim of this paper is to present the development paths of numerical investigations of cavitating flows with the use of homogeneous approach in order of publication year and with relatively detailed description. Each of the presented model is accompanied by examples of the application area. This review focuses not only on the list of the most significant existing models to predict sheet and cloud cavitation, but also on presenting their advantages and disadvantages. Moreover, it shows the reasons which inspired present authors to look for new ways of more accurate numerical predictions and dimensions of cavitation. The article includes also the division of source terms of presented models based on the transport equation with the use of standardized symbols.
Optimized Structure of the Traffic Flow Forecasting Model With a Deep Learning Approach.
Yang, Hao-Fan; Dillon, Tharam S; Chen, Yi-Ping Phoebe
2016-07-20
Forecasting accuracy is an important issue for successful intelligent traffic management, especially in the domain of traffic efficiency and congestion reduction. The dawning of the big data era brings opportunities to greatly improve prediction accuracy. In this paper, we propose a novel model, stacked autoencoder Levenberg-Marquardt model, which is a type of deep architecture of neural network approach aiming to improve forecasting accuracy. The proposed model is designed using the Taguchi method to develop an optimized structure and to learn traffic flow features through layer-by-layer feature granulation with a greedy layerwise unsupervised learning algorithm. It is applied to real-world data collected from the M6 freeway in the U.K. and is compared with three existing traffic predictors. To the best of our knowledge, this is the first time that an optimized structure of the traffic flow forecasting model with a deep learning approach is presented. The evaluation results demonstrate that the proposed model with an optimized structure has superior performance in traffic flow forecasting.
NASA Astrophysics Data System (ADS)
Babu, C. Rajesh; Kumar, P.; Rajamohan, G.
2017-07-01
Computation of fluid flow and heat transfer in an economizer is simulated by a porous medium approach, with plain tubes having a horizontal in-line arrangement and cross flow arrangement in a coal-fired thermal power plant. The economizer is a thermal mechanical device that captures waste heat from the thermal exhaust flue gasses through heat transfer surfaces to preheat boiler feed water. In order to evaluate the fluid flow and heat transfer on tubes, a numerical analysis on heat transfer performance is carried out on an 110 t/h MCR (Maximum continuous rating) boiler unit. In this study, thermal performance is investigated using the computational fluid dynamics (CFD) simulation using ANSYS FLUENT. The fouling factor ε and the overall heat transfer coefficient ψ are employed to evaluate the fluid flow and heat transfer. The model demands significant computational details for geometric modeling, grid generation, and numerical calculations to evaluate the thermal performance of an economizer. The simulation results show that the overall heat transfer coefficient 37.76 W/(m2K) and economizer coil side pressure drop of 0.2 (kg/cm2) are found to be conformity within the tolerable limits when compared with existing industrial economizer data.
Ar^+ recombination with negative ions in a flowing afterglow: A new approach.
NASA Astrophysics Data System (ADS)
Miller, Thomas M.; Viggiano, A. A.
2006-05-01
Ion-ion recombination (mutual neutralization) has been previously studied in a flowing-afterglow Langmuir-probe apparatus, using the probe to measure the positive-ion and negative-ion densities as a function of distance (time) along the flow tube axis.^1 A different approach has been taken in the present work, applicable to Ar^+ (or Kr^+ and Xe^+) recombination reactions. A flowing electron-Ar^+ afterglow plasma is first established, and the ambipolar diffusion frequency is measured. Then, an electron attaching gas is added to the afterglow, and the electron attachment rate constant and product ion branching fractions are measured in the usual manner.^2 Finally, the reactant gas concentration is reduced enough that the attachment reaction has not gone to completion by the end of the flow tube. Modeling of the diffusion, attachment, and recombination processes allows us to determine rate constants for each negative ion type recombining with Ar^+. For example, Ar^+ neutralized by Cl^-, Cl2^-, and CCl2O^- produced in attachment to oxalyl chloride,^2 shows that Cl2^- recombines at about half the rate constant of CCl2O^-, and Cl^- + Ar^+ recombination is negligible. ^1D. Smith and N. G. Adams, in Physics of Ion-Ion and Electron-Ion Collisions, Ed. F. Brouillard and J. W. McGowan (Plenum, New York, 1983). ^2J. M. Van Doren, T. M. Miller, and A. A. Viggiano, J. Chem. Phys. (submitted).
Microfluorometric Detection of Catecholamines with Multiphoton-Excited Fluorescence
NASA Astrophysics Data System (ADS)
Balaji, J.; Reddy, Chandra S.; Kaushalya, S. K.; Maiti, Sudipta
2004-04-01
We demonstrate sensitive spatially resolved detection of physiological chromophores that emit in the ultraviolet (less than 330 nm). An atypical laser source (a visible wavelength femtosecond optical parametric oscillator), and an unconventional collection geometry (a lensless detector that detects the forward-emitted fluorescence) enable this detection. We report the excitation spectra of the catecholamines dopamine and norepinephrine, together with near-UV emitters serotonin and tryptophan, in the range of 550-595 nm. We estimate the molecular two-photon action cross section of dopamine, norepinephrine, and serotonin to be 1.2 mGM (1 GM, or Goppert Mayor, is equal to 10^-58 m^4 s^-1 photon^-1), 2 mGM, and 43 mGM, respectively, at 560 nm. The sensitivity achieved by this method holds promise for the microscopic imaging of vesicular catecholamines in live cells.
Numerical solution of transonic wing flows using an Euler/Navier-Stokes zonal approach
NASA Technical Reports Server (NTRS)
Holst, T. L.; Gundy, K. L.; Thomas, S. D.; Chaderjian, N. M.; Flores, J.
1985-01-01
Transonic flow fields about wing geometries are computed using an Euler/Navier-Stokes approach in which the flow field is divided into several zones. The grid zones immediately adjacent to the wing surface are suitably clustered and solved with the Navier-Stokes equations. Grid zones removed from the wing are less finely clustered and are solved with the Euler equations. Wind tunnel wall effects are easily and accurately modeled with the new grid-zoning algorithm because the wind tunnel grid is constructed as an exact subset of the corresponding free-air grid. Solutions are obtained that are in good agreement with experiment, including cases with significant wind tunnel wall effects and shock-induced separation on the upper wing surface.
Strongly coupled partitioned approach for fluid structure interaction in free surface flows
NASA Astrophysics Data System (ADS)
Facci, Andrea Luigi; Ubertini, Stefano
2016-06-01
In this paper we describe and validate a methodology for the numerical simulation of the fluid structure interaction in free surface flows. Specifically, this study concentrates on the vertical impact of a rigid body on the water surface, (i.e. on the hull slamming problem). The fluid flow is modeled through the volume of fluid methodology, and the structure dynamics is described by the Newton's second law. An iterative algorithm guarantees the tight coupling between the fluid and solid solvers, allowing the simulations of lightweight (i.e. buoyant) structures. The methodology is validated comparing numerical results to experimental data on the free fall of different rigid wedges. The correspondence between numerical results and independent experimental findings from literature evidences the reliability and the accuracy of the proposed approach.
Analysis of dense particulate flow dynamics using a Euler-Lagrange approach
NASA Astrophysics Data System (ADS)
Desjardins, Olivier; Pepiot, Perrine
2009-11-01
Thermochemical conversion of biomass to biofuels relies heavily on dense particulate flows to enhance heat and mass transfers. While CFD tools can provide very valuable insights on reactor design and optimization, accurate simulations of these flows remain extremely challenging due to the complex coupling between the gas and solid phases. In this work, Lagrangian particle tracking has been implemented in the arbitrarily high order parallel LES/DNS code NGA [Desjardins et al., JCP, 2008]. Collisions are handled using a soft-sphere model, while a combined least squares/mollification approach is adopted to accurately transfer data between the Lagrangian particles and the Eulerian gas phase mesh, regardless of the particle diameter to mesh size ratio. The energy conservation properties of the numerical scheme are assessed and a detailed statistical analysis of the dynamics of a periodic fluidized bed with a uniform velocity inlet is conducted.
Application of the mobility power flow approach to structural response from distributed loading
NASA Technical Reports Server (NTRS)
Cuschieri, J. M.
1988-01-01
The problem of the vibration power flow through coupled substructures when one of the substructures is subjected to a distributed load is addressed. In all the work performed thus far, point force excitation was considered. However, in the case of the excitation of an aircraft fuselage, distributed loading on the whole surface of a panel can be as important as the excitation from directly applied forces at defined locations on the structures. Thus using a mobility power flow approach, expressions are developed for the transmission of vibrational power between two coupled plate substructures in an L configuration, with one of the surfaces of one of the plate substructures being subjected to a distributed load. The types of distributed loads that are considered are a force load with an arbitrary function in space and a distributed load similar to that from acoustic excitation.
A time-dependent approach for calculating steady inverse boundary-layer flows with separation
NASA Technical Reports Server (NTRS)
Cebeci, T.
1983-01-01
An unsteady inverse boundary-layer method is developed which can be used to calculate steady flows with separation. Two versions of Keller's box method with the Mechul function formulation developed by Cebeci (1976) are employed, depending on the complexity of the flow. The regular box is employed in regions of positive streamwise velocity component u, whereas the zigzag box is employed in regions where u becomes negative (t greater than 0). The regular box with the FLARE approximation is employed when t = 0 and u becomes negative in some region across the layer. Results of calculations show that the use of a time-dependent inverse boundary-layer method in which time is used as an iteration parameter provides a good approach in improving the accuracy of the solutions obtained from the FLARE approximation.
Ababou, R.
1991-08-01
This report develops a broad review and assessment of quantitative modeling approaches and data requirements for large-scale subsurface flow in radioactive waste geologic repository. The data review includes discussions of controlled field experiments, existing contamination sites, and site-specific hydrogeologic conditions at Yucca Mountain. Local-scale constitutive models for the unsaturated hydrodynamic properties of geologic media are analyzed, with particular emphasis on the effect of structural characteristics of the medium. The report further reviews and analyzes large-scale hydrogeologic spatial variability from aquifer data, unsaturated soil data, and fracture network data gathered from the literature. Finally, various modeling strategies toward large-scale flow simulations are assessed, including direct high-resolution simulation, and coarse-scale simulation based on auxiliary hydrodynamic models such as single equivalent continuum and dual-porosity continuum. The roles of anisotropy, fracturing, and broad-band spatial variability are emphasized. 252 refs.
Exact Solutions for Stokes' Flow of a Non-Newtonian Nanofluid Model: A Lie Similarity Approach
NASA Astrophysics Data System (ADS)
Aziz, Taha; Aziz, A.; Khalique, C. M.
2016-07-01
The fully developed time-dependent flow of an incompressible, thermodynamically compatible non-Newtonian third-grade nanofluid is investigated. The classical Stokes model is considered in which the flow is generated due to the motion of the plate in its own plane with an impulsive velocity. The Lie symmetry approach is utilised to convert the governing nonlinear partial differential equation into different linear and nonlinear ordinary differential equations. The reduced ordinary differential equations are then solved by using the compatibility and generalised group method. Exact solutions for the model equation are deduced in the form of closed-form exponential functions which are not available in the literature before. In addition, we also derived the conservation laws associated with the governing model. Finally, the physical features of the pertinent parameters are discussed in detail through several graphs.
Analysis of Different Approaches to Modeling of Nozzle Flows in the Near Continuum Regime
NASA Astrophysics Data System (ADS)
Titov, E. V.; Kumar, Rakesh; Levin, D. A.; Gimelshein, N. E.; Gimelshein, S. F.
2008-12-01
Conical nozzle flows are studied for Reynolds numbers of 1,230 and 12,300 using different numerical techniques: DSMC Method, Navier-Stokes/CFD accounting for velocity slip and temperature jump boundary conditions, and statistical and deterministic approaches to the solution of BGK equation. Detailed comparison of the stability, accuracy, and convergence of the employed numerical techniques provides better understanding of their benefits and deficiencies, and assists in selecting the most appropriate technique for a particular nozzle and flow application. The deterministic and statistical solutions of the BGK equation were found to be in good agreement with the benchmark DSMC results. The Navier-Stokes solution differs from DSMC in the boundary layer.
A hybrid least squares support vector machines and GMDH approach for river flow forecasting
NASA Astrophysics Data System (ADS)
Samsudin, R.; Saad, P.; Shabri, A.
2010-06-01
This paper proposes a novel hybrid forecasting model, which combines the group method of data handling (GMDH) and the least squares support vector machine (LSSVM), known as GLSSVM. The GMDH is used to determine the useful input variables for LSSVM model and the LSSVM model which works as time series forecasting. In this study the application of GLSSVM for monthly river flow forecasting of Selangor and Bernam River are investigated. The results of the proposed GLSSVM approach are compared with the conventional artificial neural network (ANN) models, Autoregressive Integrated Moving Average (ARIMA) model, GMDH and LSSVM models using the long term observations of monthly river flow discharge. The standard statistical, the root mean square error (RMSE) and coefficient of correlation (R) are employed to evaluate the performance of various models developed. Experiment result indicates that the hybrid model was powerful tools to model discharge time series and can be applied successfully in complex hydrological modeling.
Computation of transonic separated wing flows using an Euler/Navier-Stokes zonal approach
NASA Technical Reports Server (NTRS)
Kaynak, Uenver; Holst, Terry L.; Cantwell, Brian J.
1986-01-01
A computer program called Transonic Navier Stokes (TNS) has been developed which solves the Euler/Navier-Stokes equations around wings using a zonal grid approach. In the present zonal scheme, the physical domain of interest is divided into several subdomains called zones and the governing equations are solved interactively. The advantages of the Zonal Grid approach are as follows: (1) the grid for any subdomain can be generated easily; (2) grids can be, in a sense, adapted to the solution; (3) different equation sets can be used in different zones; and, (4) this approach allows for a convenient data base organization scheme. Using this code, separated flows on a NACA 0012 section wing and on the NASA Ames WING C have been computed. First, the effects of turbulence and artificial dissipation models incorporated into the code are assessed by comparing the TNS results with other CFD codes and experiments. Then a series of flow cases is described where data are available. The computed results, including cases with shock-induced separation, are in good agreement with experimental data. Finally, some futuristic cases are presented to demonstrate the abilities of the code for massively separated cases which do not have experimental data.
NASA Astrophysics Data System (ADS)
Bok, Tae-Hoon; Hysi, Eno; Kolios, Michael C.
2017-03-01
In the present paper, the optical wavelength dependence on the photoacoustic (PA) assessment of the pulsatile blood flow was investigated by means of the experimental and theoretical approaches analyzing PA radiofrequency spectral parameters such as the spectral slope (SS) and mid-band fit (MBF). For the experimental approach, the pulsatile flow of human whole blood at 60 bpm was imaged using the VevoLAZR system (40-MHz-linear-array probe, 700-900 nm illuminations). For the theoretical approach, a Monte Carlo simulation for the light transmit into a layered tissue phantom and a Green's function based method for the PA wave generation was implemented for illumination wavelengths of 700, 750, 800, 850 and 900 nm. The SS and MBF for the experimental results were compared to theoretical ones as a function of the illumination wavelength. The MBF increased with the optical wavelength in both theory and experiments. This was expected because the MBF is representative of the PA magnitude, and the PA signal from red blood cell (RBC) is dependent on the molar extinction coefficient of oxyhemoglobin. On the other hand, the SS decreased with the wavelength, even though the RBC size (absorber size which is related to the SS) cannot depend on the illumination wavelength. This conflicting result can be interpreted by means of the changes of the fluence pattern for different illumination wavelengths. The SS decrease with the increasing illumination wavelength should be further investigated.
Thick plate bending wave transmission using a mobility power flow approach
NASA Technical Reports Server (NTRS)
Mccollum, M. D.; Cuschieri, J. M.
1990-01-01
The mobility power flow (MPF) approach is used in this paper to describe the flexural behavior of an L-shaped plate structure consisting of thick plates with rotary inertia and shear deformation effects included in the analysis. The introduction of the thick plate effects significantly increases the complexity of the structural mobility functions used in the definitions of the power flow terms; however, because of the substructuring that is used in the MPF approach, the complexity of the problem is significantly reduced as compared to solving for the global structure. Additionally, with the MPF approach the modal behavior is described. The MPF analysis of the L-shaped plate is performed for the case of point force excitation on one plate, with the two plates being identical in both size and thickness. The results of this analysis are compared to results from the finite-element analysis (FEA) and the statistical energy analysis (SEA) and show very good agreement in the low- and high-frequency regimes, respectively.
Thick plate bending wave transmission using a mobility power flow approach
NASA Technical Reports Server (NTRS)
Mccollum, M. D.; Cuschieri, J. M.
1990-01-01
The mobility power flow (MPF) approach is used in this paper to describe the flexural behavior of an L-shaped plate structure consisting of thick plates with rotary inertia and shear deformation effects included in the analysis. The introduction of the thick plate effects significantly increases the complexity of the structural mobility functions used in the definitions of the power flow terms; however, because of the substructuring that is used in the MPF approach, the complexity of the problem is significantly reduced as compared to solving for the global structure. Additionally, with the MPF approach the modal behavior is described. The MPF analysis of the L-shaped plate is performed for the case of point force excitation on one plate, with the two plates being identical in both size and thickness. The results of this analysis are compared to results from the finite-element analysis (FEA) and the statistical energy analysis (SEA) and show very good agreement in the low- and high-frequency regimes, respectively.
NASA Astrophysics Data System (ADS)
Yuan, Yao-Ming; Jiang, Rui; Hu, Mao-Bin; Wu, Qing-Song; Wang, Ruili
2009-06-01
In this paper, we have investigated traffic flow characteristics in a traffic system consisting of a mixture of adaptive cruise control (ACC) vehicles and manual-controlled (manual) vehicles, by using a hybrid modelling approach. In the hybrid approach, (i) the manual vehicles are described by a cellular automaton (CA) model, which can reproduce different traffic states (i.e., free flow, synchronised flow, and jam) as well as probabilistic traffic breakdown phenomena; (ii) the ACC vehicles are simulated by using a car-following model, which removes artificial velocity fluctuations due to intrinsic randomisation in the CA model. We have studied the traffic breakdown probability from free flow to congested flow, the phase transition probability from synchronised flow to jam in the mixed traffic system. The results are compared with that, where both ACC vehicles and manual vehicles are simulated by CA models. The qualitative and quantitative differences are indicated.
A three-pillar approach to assessing climate impacts on low flows
NASA Astrophysics Data System (ADS)
Laaha, Gregor; Parajka, Juraj; Viglione, Alberto; Koffler, Daniel; Haslinger, Klaus; Schöner, Wolfgang; Zehetgruber, Judith; Blöschl, Günter
2016-09-01
The objective of this paper is to present a framework for assessing climate impacts on future low flows that combines different sources of information, termed pillars. To illustrate the framework three pillars are chosen: (a) extrapolation of observed low-flow trends into the future, (b) rainfall-runoff projections based on climate scenarios and (c) extrapolation of changing stochastic rainfall characteristics into the future combined with rainfall-runoff modelling. Alternative pillars could be included in the overall framework. The three pillars are combined by expert judgement based on a synoptic view of data, model outputs and process reasoning. The consistency/inconsistency between the pillars is considered an indicator of the certainty/uncertainty of the projections. The viability of the framework is illustrated for four example catchments from Austria that represent typical climate conditions in central Europe. In the Alpine region where winter low flows dominate, trend projections and climate scenarios yield consistently increasing low flows, although of different magnitudes. In the region north of the Alps, consistently small changes are projected by all methods. In the regions in the south and south-east, more pronounced and mostly decreasing trends are projected but there is disagreement in the magnitudes of the projected changes. The process reasons for the consistencies/inconsistencies are discussed. For an Alpine region such as Austria the key to understanding low flows is whether they are controlled by freezing and snowmelt processes, or by the summer moisture deficit associated with evaporation. It is argued that the three-pillar approach offers a systematic framework of combining different sources of information aimed at more robust projections than that obtained from each pillar alone.
Quantification of non-stormwater flow entries into storm drains using a water balance approach.
Xu, Zuxin; Yin, Hailong; Li, Huaizheng
2014-07-15
To make decisions about correcting illicit or inappropriate connections to storm drains, quantification of non-stormwater entries into storm drains was performed using a water flow balance approach, based on data analysis from 2008 to 2011 in a separate storm drainage system in a Shanghai downtown area of 374 ha. The study revealed severe sewage connections to storm drains; meanwhile, misconnections between surface water and storm drains were found to drive frequent non-stormwater pumping discharges at the outfall, producing a much larger volume of outfall flows in a short period. This paper presented a methodology to estimate quantities of inappropriate sewage flow, groundwater infiltration and river water backflow into the storm drains. It was concluded that inappropriate sewage discharge and groundwater seepage into storm drains were approximately 17,860 m(3)/d (i.e., up to 51% of the total sewage flow in the catchment) and 3,624 m(3)/d, respectively, and surface water backflow was up to an average 28,593 m(3)/d. On the basis of this work, end-of-storm pipe interceptor sewers of 0.25 m(3)/s (i.e., 21,600 m(3)/d) would be effective to tackle the problem of sewage connections and groundwater seepage to storm drains. Under this circumstance, the follow-up non-stormwater outfall pumping events indicate misconnections between surface water and storm drains, featuring pumping discharge equivalent to surface water backflow; hence the misconnections should be repaired. The information provided here is helpful in estimating the magnitude of non-stormwater flow entries into storm drains and designing the necessary pollution control activities, as well as combating city floods in storm events. Copyright © 2014. Published by Elsevier B.V.
Flow-through SIP - A novel stable isotope probing approach limiting cross-feeding
NASA Astrophysics Data System (ADS)
Mooshammer, Maria; Kitzinger, Katharina; Schintlmeister, Arno; Kjedal, Henrik; Nielsen, Jeppe Lund; Nielsen, Per; Wagner, Michael
2017-04-01
Stable isotope probing (SIP) is a widely applied tool to link specific microbial populations to metabolic processes in the environment without the prerequisite of cultivation, which has greatly advanced our understanding of the role of microorganisms in biogeochemical cycling. SIP relies on tracing specific isotopically labeled substrates (e.g., 13C, 15N, 18O) into cellular biomarkers, such as DNA, RNA or phospholipid fatty acids, and is considered to be a robust technique to identify microbial populations that assimilate the labeled substrate. However, cross-feeding can occur when labeled metabolites are released from a primary consumer and then used by other microorganisms. This leads to erroneous identification of organisms that are not directly responsible for the process of interest, but are rather connected to primary consumers via a microbial food web. Here, we introduce a new approach that has the potential to eliminate the effect of cross-feeding in SIP studies and can thus also be used to distinguish primary consumers from other members of microbial food webs. In this approach, a monolayer of microbial cells are placed on a filter membrane, and labeled substrates are supplied by a continuous flow. By means of flow-through, labeled metabolites and degradation products are constantly removed, preventing secondary consumption of the substrate. We present results from a proof-of-concept experiment using nitrifiers from activated sludge as model system, in which we used fluorescence in situ hybridization (FISH) with rRNA-targeted oligonucleotide probes for identification of nitrifiers in combination with nanoscale secondary ion mass spectrometry (NanoSIMS) for visualization of isotope incorporation at the single-cell level. Our results show that flow-through SIP is a promising approach to significantly reduce cross-feeding and secondary substrate consumption in SIP experiments.
Coordinated Sampling: An Efficient, Network-Wide Approach for Flow Monitoring
2007-07-16
corresponding PoP-level paths. For Internet2 and GÉANT we rely on the publicly available static IS-IS weights and for the Rocketfuel-based topologies we...13225 80 320 AS2914 70 4900 51 204 AS3356 63 3969 46 196 AS1239 52 2704 37 148 AS1221 44 1936 32 128 AS3257 41 1681 32 218 GÉANT 22 484 16 64 Internet2 ...cial ISPs, we take the following approach. Taking 8 million IP flows (per 5-minute interval)5 as the baseline traffic volume for Internet2 , for each the
A Multiblock Approach for Calculating Incompressible Fluid Flows on Unstructured Grids
NASA Technical Reports Server (NTRS)
Sheng, Chunhua; Whitfield, David L.; Anderson, W. Kyle
1997-01-01
A multiblock approach is presented for solving two-dimensional incompressible turbulent flows on unstructured grids. The artificial compressibility form of the governing equations is solved by a vertex-centered, finite-volume implicit scheme which uses a backward Euler time discretization. Point Gauss-Seidel relaxations are used to solve the linear system of equations at each time step. This work introduces a multiblock strategy to the solution procedure, which greatly improves the efficiency of the algorithm by significantly reducing the memory requirements while not increasing the CPU time. Results presented in this work shows that the current multiblock algorithm requires 70% less memory than the single block algorithm.
Computing 3-D steady supersonic flow via a new Lagrangian approach
NASA Technical Reports Server (NTRS)
Loh, C. Y.; Liou, M.-S.
1993-01-01
The new Lagrangian method introduced by Loh and Hui (1990) is extended for 3-D steady supersonic flow computation. Details of the conservation form, the implementation of the local Riemann solver, and the Godunov and the high resolution TVD schemes are presented. The new approach is robust yet accurate, capable of handling complicated geometry and reactions between discontinuous waves. It keeps all the advantages claimed in the 2-D method of Loh and Hui, e.g., crisp resolution for a slip surface (contact discontinuity) and automatic grid generation along the stream.
DCT-TCI: Real Gas Characterization of Plasma Flow Control - An Integrated Approach
2011-12-23
code) 23-12-2011 Final 1 June 2009 - 30 November 2011 DCT- TCI : Real Gas Characterization of Plasma Flow Control-An Integrated Approach FA9550-09-1...Geometry, Multi-Barrier Plasma Actuators, Stereo PIV Experiment, MIG Plasma Kinetic Simulation U U U U 18 Dr. S Roy 352-392-9823 Reset 1 DCT- TCI ...chamber shown in FIG. 6a. The floor of the chamber is connected to a single axis manual traverse (Velmex A1503P40-S1.5), which allows the floor to
Computing 3-D steady supersonic flow via a new Lagrangian approach
NASA Technical Reports Server (NTRS)
Loh, C. Y.; Liou, M.-S.
1993-01-01
The new Lagrangian method introduced by Loh and Hui (1990) is extended for 3-D steady supersonic flow computation. Details of the conservation form, the implementation of the local Riemann solver, and the Godunov and the high resolution TVD schemes are presented. The new approach is robust yet accurate, capable of handling complicated geometry and reactions between discontinuous waves. It keeps all the advantages claimed in the 2-D method of Loh and Hui, e.g., crisp resolution for a slip surface (contact discontinuity) and automatic grid generation along the stream.
a Novel Approach for Analyzing Supersonic High Reynolds Number Flows with Separation.
NASA Astrophysics Data System (ADS)
Power, Gregory Dan
A phenomenon which can have a significant impact on the performance of supersonic and hypersonic vehicles and their propulsion systems is the strong interaction which occurs between the viscous and inviscid regions of high Reynolds number, laminar flows. Strong interaction is characterized by the presence of "upstream influence" and often results in flow separation. Since strong viscous/inviscid interaction can significantly alter the flow field and degrade the performance of airframe and propulsion systems, accurately predicting these flows is essential to the aerodynamic design process. The goal of the present study is to develop a physically based computational technique to solve the steady Navier-Stokes equations for the above class of problems. This goal is accomplished by tailoring the analysis to reflect the dominant mechanism of strong viscous/inviscid interaction as determined from experimental observations and mathematical theories. A reduced set of composite equations, derived from the full Navier-Stokes equations, is solved in a globally -iterated, space-marching manner where upstream influence is modelled through the introduction of the stream function along a single line oriented in the streamwise direction and located within the viscous region. This novel technique for solving the composite equations represents an extension of established two-layer interacting viscous-layer approaches and should be applicable to a broader range of flow conditions than the two-layer methods while providing a comparable level of efficiency and thus could provide an effective alternative to time-marching algorithms. Computational results are presented for the cases of normal slot injection into a supersonic stream and shock/boundary -layer interaction with and without separation. These results compare favorably with results computed using an asymptotic analysis, results computed using a time-marching Navier -Stokes procedure, and available experimental data. In addition
State of the Art High-Throughput Approaches to Genotoxicity: Flow Micronucleus, Ames II, GreenScreen and Comet (Presented by Dr. Marilyn J. Aardema, Chief Scientific Advisor, Toxicology, Dr. Leon Stankowski, et. al. (6/28/2012)
Horizontal annular flow modelling using a compositional based interface capturing approach
NASA Astrophysics Data System (ADS)
Pavlidis, Dimitrios; Xie, Zhizhua; Percival, James; Gomes, Jefferson; Pain, Chris; Matar, Omar
2014-11-01
Progress on a consistent approach for interface-capturing in which each component represents a different phase/fluid is described. The aim is to develop a general multi-phase modelling approach based on fully-unstructured meshes that can exploit the latest mesh adaptivity methods, and in which each fluid phase may have a number of components. The method is compared against experimental results for a collapsing water column test case and a convergence study is performed. A number of numerical test cases are undertaken to demonstrate the method's ability to model arbitrary numbers of phases with arbitrary equations of state. The method is then used to simulate horizontal annular flows. EPSRC Programme Grant, MEMPHIS, EP/K0039761/1.
Sevov, Christo S; Hickey, David P; Cook, Monique E; Robinson, Sophia G; Barnett, Shoshanna; Minteer, Shelley D; Sigman, Matthew S; Sanford, Melanie S
2017-03-01
The deployment of nonaqueous redox flow batteries for grid-scale energy storage has been impeded by a lack of electrolytes that undergo redox events at as low (anolyte) or high (catholyte) potentials as possible while exhibiting the stability and cycling lifetimes necessary for a battery device. Herein, we report a new approach to electrolyte design that uses physical organic tools for the predictive targeting of electrolytes that possess this combination of properties. We apply this approach to the identification of a new pyridinium-based anolyte that undergoes 1e(-) electrochemical charge-discharge cycling at low potential (-1.21 V vs Fc/Fc(+)) to a 95% state-of-charge without detectable capacity loss after 200 cycles.
Use split-flow approach to speed patients to needed care, eliminate inefficiencies and duplication.
2013-05-01
To address time and space challenges in the midst of surging demand, the ED at St. Mary Medical Center in Langhorne, PA, turned to the split-flow model, an evidence-based practice that relies heavily on the queuing theory to improve patient throughput. In less than one year, the approach has enabled administrators to reduce door-to-physician times from an average of 47 minutes to 23.5 minutes, and overall length-of-stay in the ED for discharged patients has been slashed by 21 minutes. Under the split-flow system implemented at St. Mary, an expedited triage/assessment process directs patients to prompt care, pediatric care, acute care, or an expedited treatment area (ETA) where patients will undergo further testing or procedures. This initial assessment typically takes about three minutes. Patients sent to the ETA remain there for no longer than 30 minutes.They may then be moved to a holding area while awaiting test results. Patients are constantly moving in the split-flow model, so it is important to pay close attention to handoffs. Patients will begin the process with one nurse and finish with another.
NASA Astrophysics Data System (ADS)
Dhir, Gaurav; Suman, Sawan
2015-11-01
Experimental evidence shows that aircrafts operating under heavy rainfall conditions face deterioration of lift and increase in drag. This scenario can be a critical design challenge especially for slow moving vehicles such as airships. Effective roughening of airfoil surface caused by an uneven water film, loss of flow momentum and the loss of vehicle momentum due to its collision with the raindrops are the primary reasons causing the drag to increase. Our work focuses primarily on the numerical quantification of boundary layer momentum loss caused due to raindrops. The collision of raindrops with a solid surface leads to formation of an ejecta fog of splashed back droplets with their sizes being of the order of micrometers and their acceleration leads to boundary layer momentum loss. We model the airflow within a flat plate boundary layer using a Lagrangian-Eulerian approach with the raindrops being considered as non-deformable, non-spinning and non-interacting droplets. We employ an inter-phase coupling term to account for the interaction between the boundary layer flow and the droplets. Our presentation will focus on several comparisons (velocity field, lift and drag at various angles of attack) with the results of the standard (rain-free) Prandtl boundary layer flow. Indian Institute of Technology, Delhi.
Mehregan, Forough; Tournoux, François; Muth, Stéphan; Pibarot, Philippe; Rieu, Régis; Cloutier, Guy; Garcia, Damien
2013-01-01
We propose a new approach for quantification of intracardiac vorticity – Doppler vortography – based on conventional color Doppler images. Doppler vortography relies on the centrosymmetric properties of the vortices. Such properties induce particular symmetries in the Doppler flow data which can be exploited to describe the vortices quantitatively. For this purpose, a kernel filter was developed to derive a parameter –the blood vortex signature (BVS) – that allows detecting the main intracardiac vortices and estimating their core vorticities. The reliability of Doppler vortography was assessed in mock Doppler fields issued from simulations and in vitro data. Doppler vortography was also tested in patients and compared with vector flow mapping by echocardiography. Strong correlations were obtained between the Doppler vortography-derived and the ground-truth vorticities (in silico: r2 = 0.98, in vitro: r2 = 0.86, in vivo: r2 = 0.89). Our results demonstrated that Doppler vortography is a potentially promising echocardiographic tool for quantification of vortex flow in the left ventricle. PMID:24210865
A Lagrangian approach to study flow topology around a flapping flat-plate wing
NASA Astrophysics Data System (ADS)
Krishna, Swathi; Mulleners, Karen; Green, Melissa
2015-11-01
The incredible flight performance of insects can be attributed in part to the generation and maintenance of stable regions of vorticity, which is achieved by manipulating the wing kinematics. Along with the prolonged attachment of the leading edge vortex during translation of the wing, the rotational motion at the end of the stroke is critical as it generates large amounts of lift required for the insect to remain air-borne while hovering. The wing reversal entails a change in the flow-field around the wing which is closely tied to variations in force production. Based on phase-averaged particle image velocimetry data we analyze the effect of a shift in the rotational phase of a flapping wing on the flow characteristics. A topological study is conducted using Lagrangian vortex detection techniques in order to characterize the shear layer formation, vortex interactions and flow separation. The Lagrangian analysis includes the calculation of Finite Time Lyapunov Exponents based on particle trajectories. An objective approach is employed to trace the location of separation or attachment points as an indication for changes in the strength, stability and shedding frequencies of vortices. These trajectories are correlated with fluctuations in aerodynamic force coefficients.
Martínez, Amparo; Manunza, Arianna; Delgado, Juan Vicente; Landi, Vincenzo; Adebambo, Ayotunde; Ismaila, Muritala; Capote, Juan; El Ouni, Mabrouk; Elbeltagy, Ahmed; Abushady, Asmaa M.; Galal, Salah; Ferrando, Ainhoa; Gómez, Mariano; Pons, Agueda; Badaoui, Bouabid; Jordana, Jordi; Vidal, Oriol; Amills, Marcel
2016-01-01
Human-driven migrations are one of the main processes shaping the genetic diversity and population structure of domestic species. However, their magnitude and direction have been rarely analysed in a statistical framework. We aimed to estimate the impact of migration on the population structure of Spanish and African goats. To achieve this goal, we analysed a dataset of 1,472 individuals typed with 23 microsatellites. Population structure of African and Spanish goats was moderate (mean FST = 0.07), with the exception of the Canarian and South African breeds that displayed a significant differentiation when compared to goats from North Africa and Nigeria. Measurement of gene flow with Migrate-n and IMa coalescent genealogy samplers supported the existence of a bidirectional gene flow between African and Spanish goats. Moreover, IMa estimates of the effective number of migrants were remarkably lower than those calculated with Migrate-n and classical approaches. Such discrepancies suggest that recent divergence, rather than extensive gene flow, is the main cause of the weak population structure observed in caprine breeds. PMID:27966592
Bubble-induced turbulence study in homogeneous turbulent flow using DNS approach
NASA Astrophysics Data System (ADS)
Feng, Jinyong; Bolotnov, Igor
2015-11-01
The effect of a single bubble on the energy transfer to a homogeneous turbulent flow using DNS approach is investigated for various conditions. The single-phase turbulence is numerically generated by pressure-gradient driven uniform flow through a fully resolved turbulence generating grid. The turbulent intensity measured is uniform normal to the flow direction. The decay rate of the turbulent kinetic energy is validated against analytical power law. The collected instantaneous velocity is used as inflow condition for single-bubble simulations to study the bubble-induced turbulence (BIT). In interface-resolved two-phase simulation the bubble is kept at fixed positions by using a proportional-integral-derivative controller. This simulation set allows estimating the turbulent kinetic energy before and after the bubble, quantifying the BIT. Effects of bubble deformability, velocity and turbulent intensity are separately studied. We observe that for a nearly spherical bubble, the bubble-induced turbulence is positive, increasing the level of turbulent kinetic energy in the liquid phase. BIT is influenced by the other studied parameters and the presented work will contribute to the closure BIT model development in multiphase computational fluid dynamics modeling. The work is supported by NSF-CBET-Fluid Dynamics, Award #1333993.
Runoff modelling using radar data and flow measurements in a stochastic state space approach.
Krämer, S; Grum, M; Verworn, H R; Redder, A
2005-01-01
In urban drainage the estimation of runoff with the help of models is a complex task. This is in part due to the fact that rainfall, the most important input to urban drainage modelling, is highly uncertain. Added to the uncertainty of rainfall is the complexity of performing accurate flow measurements. In terms of deterministic modelling techniques these are needed for calibration and evaluation of the applied model. Therefore, the uncertainties of rainfall and flow measurements have a severe impact on the model parameters and results. To overcome these problems a new methodology has been developed which is based on simple rain plane and runoff models that are incorporated into a stochastic state space model approach. The state estimation is done by using the extended Kalman filter in combination with a maximum likelihood criterion and an off-line optimization routine. This paper presents the results of this new methodology with respect to the combined consideration of uncertainties in distributed rainfall derived from radar data and uncertainties in measured flows in an urban catchment within the Emscher river basin, Germany.
Estimation of turbulent channel flow based on the wall measurement with a statistical approach
NASA Astrophysics Data System (ADS)
Hasegawa, Yosuke; Suzuki, Takao
2016-11-01
A turbulent channel flow at Ret au = 100 with periodic boundary conditions is estimated with linear stochastic estimation only based on the wall measurement, i.e. the shear-stress in the streamwise and spanwise directions as well as the pressure over the entire wavenumbers. The results reveal that instantaneous measurement on the wall governs the success of the estimation in y+ < 20. Degrees of agreement are equivalent to those reported by Chevalier et al. (2006) using a data-assimilation approach. This suggests that the instantaneous wall information dictates the estimation rather than the estimator solving the dynamical system. We feed the velocity components from the linear stochastic estimation via the body-force term into the Navier-Stokes system; however, the estimation slightly improves in the log layer, indicating some benefit of involving a dynamical system but over-suppression of turbulent kinetic energy beyond the viscous sublayer by the linear stochastic estimation. Motions inaccurately estimated in the buffer layer prevent from further reconstruction toward the centerline even if we relax the feedback forcing and let the flow evolve nonlinearly through the estimator. We also argue the inherent limitation of turbulent flow estimation based on the wall measurement.
Martínez, Amparo; Manunza, Arianna; Delgado, Juan Vicente; Landi, Vincenzo; Adebambo, Ayotunde; Ismaila, Muritala; Capote, Juan; El Ouni, Mabrouk; Elbeltagy, Ahmed; Abushady, Asmaa M; Galal, Salah; Ferrando, Ainhoa; Gómez, Mariano; Pons, Agueda; Badaoui, Bouabid; Jordana, Jordi; Vidal, Oriol; Amills, Marcel
2016-12-14
Human-driven migrations are one of the main processes shaping the genetic diversity and population structure of domestic species. However, their magnitude and direction have been rarely analysed in a statistical framework. We aimed to estimate the impact of migration on the population structure of Spanish and African goats. To achieve this goal, we analysed a dataset of 1,472 individuals typed with 23 microsatellites. Population structure of African and Spanish goats was moderate (mean FST = 0.07), with the exception of the Canarian and South African breeds that displayed a significant differentiation when compared to goats from North Africa and Nigeria. Measurement of gene flow with Migrate-n and IMa coalescent genealogy samplers supported the existence of a bidirectional gene flow between African and Spanish goats. Moreover, IMa estimates of the effective number of migrants were remarkably lower than those calculated with Migrate-n and classical approaches. Such discrepancies suggest that recent divergence, rather than extensive gene flow, is the main cause of the weak population structure observed in caprine breeds.
NASA Astrophysics Data System (ADS)
Han, Zheng; Chen, Guangqi; Li, Yange; Wang, Wei; Zhang, Hong
2015-07-01
The estimation of debris-flow velocity in a cross-section is of primary importance due to its correlation to impact force, run up and superelevation. However, previous methods sometimes neglect the observed asymmetric velocity distribution, and consequently underestimate the debris-flow velocity. This paper presents a new approach for exploring the debris-flow velocity distribution in a cross-section. The presented approach uses an iteration algorithm based on the Riemann integral method to search an approximate solution to the unknown flow surface. The established laws for vertical velocity profile are compared and subsequently integrated to analyze the velocity distribution in the cross-section. The major benefit of the presented approach is that natural channels typically with irregular beds and superelevations can be taken into account, and the resulting approximation by the approach well replicates the direct integral solution. The approach is programmed in MATLAB environment, and the code is open to the public. A well-documented debris-flow event in Sichuan Province, China, is used to demonstrate the presented approach. Results show that the solutions of the flow surface and the mean velocity well reproduce the investigated results. Discussion regarding the model sensitivity and the source of errors concludes the paper.
NASA Astrophysics Data System (ADS)
Manners, R.; Wilcox, A. C.; Merritt, D. M.
2016-12-01
The ecogeomorphic response of riparian ecosystems to a change in hydrologic properties is difficult to predict because of the interactions and feedbacks among plants, water, and sediment. Most riparian models of community dynamics assume a static channel, yet geomorphic processes strongly control the establishment and survival of riparian vegetation. Using a combination of approaches that includes empirical relationships and hydrodynamic models, we model the coupled vegetation-topographic response of three cross-sections on the Yampa and Green Rivers in Dinosaur National Monument, to a shift in the flow regime. The locations represent the variable geomorphology and vegetation composition of these canyon-bound rivers. We account for the inundation and hydraulic properties of vegetation plots surveyed over three years within International River Interface Cooperative (iRIC) Fastmech, equipped with a vegetation module that accounts for flexible stems and plant reconfiguration. The presence of functional groupings of plants, or those plants that respond similarly to environmental factors such as water availability and disturbance are determined from flow response curves developed for the Yampa River. Using field measurements of vegetation morphology, distance from the channel centerline, and dominant particle size and modeled inundation properties we develop an empirical relationship between these variables and topographic change. We evaluate vegetation and channel form changes over decadal timescales, allowing for the integration of processes over time. From our analyses, we identify thresholds in the flow regime that alter the distribution of plants and reduce geomorphic complexity, predominately through side-channel and backwater infilling. Simplification of some processes (e.g., empirically-derived sedimentation) and detailed treatment of others (e.g., plant-flow interactions) allows us to model the coupled dynamics of riparian ecosystems and evaluate the impact of
An adaptive level set approach for incompressible two-phase flows
Sussman, M.; Almgren, A.S.; Bell, J.B.
1997-04-01
In Sussman, Smereka and Osher, a numerical method using the level set approach was formulated for solving incompressible two-phase flow with surface tension. In the level set approach, the interface is represented as the zero level set of a smooth function; this has the effect of replacing the advection of density, which has steep gradients at the interface, with the advection of the level set function, which is smooth. In addition, the interface can merge or break up with no special treatment. The authors maintain the level set function as the signed distance from the interface in order to robustly compute flows with high density ratios and stiff surface tension effects. In this work, they couple the level set scheme to an adaptive projection method for the incompressible Navier-Stokes equations, in order to achieve higher resolution of the interface with a minimum of additional expense. They present two-dimensional axisymmetric and fully three-dimensional results of air bubble and water drop computations.
Quantifying Vadose Zone Flow and Transport Uncertainties Using a Unified, Hierarchical Approach
Meyer, Philip D.; Murray, Christopher J.; Rockhold, Mark L.; Schaap, Marcel
2002-06-01
The objective of this research is to develop and demonstrate a general approach for modeling flow and transport in the heterogeneous vadose zone. The approach uses similar media scaling, geostatistics, and conditional simulation methods to estimate soil hydraulic parameters at unsampled locations from field-measured water content data and scale-mean hydraulic parameters determined from available site characterization data. Neural network methods are being developed to estimate soil hydraulic parameters from more easily measured physical property data such as bulk density, organic matter content, and percentages of sand, silt, and clay (or particle-size distributions). Field water content distributions are being estimated using various geophysical methods including neutron moderation, ground-penetrating radar, and electrical resistance tomography. One of the primary goals of this research is to determine relationships between the type of data used in model parameterization, the quantity of data available, the scale of the measurement, and the uncertainty in predictions of flow and transport using these methods. Evaluation of the relationships between available data, scale, and uncertainty are using data from a large-scale, controlled field experiment.
Quantifying Vadose Zone Flow and Transport Uncertainties Using a Unified, Hierarchical Approach
Meyer, Philip D.; Murray, Chris J.; Rockhold, Mark L.
2001-06-01
The objective of this research is to develop and demonstrate a general approach for modeling flow and transport in the heterogeneous vadose zone. The approach uses similar media scaling, geostatistics, and conditional simulation methods to estimate soil hydraulic parameters at unsampled locations from field-measured water content data and scale-mean hydraulic parameters determined from available site characterization data. Neural network methods are being developed to estimate soil hydraulic parameters from more easily measured physical property data such as bulk density, organic matter content, and percentages of sand, silt, and clay (or particle-size distributions). Field water content distributions are being estimated using various geophysical methods including neutron moderation, ground-penetrating radar, and electrical resistance tomography. One of the primary goals of this research is to determine relationships between the type of data used in model parameterization, th e quantity of data available, the scale of the measurement, and the uncertainty in predictions of flow and transport using these methods. Evaluation of the relationships between available data, scale, and uncertainty will use primarily existing data from large-scale, controlled experiments.
Solution-Adaptive Cartesian Cell Approach for Viscous and Inviscid Flows
NASA Technical Reports Server (NTRS)
Coirier, William J.; Powell, Kenneth G.
1996-01-01
A Cartesian cell-based approach for adaptively refined solutions of the Euler and Navier-Stokes equations in two dimensions is presented. Grids about geometrically complicated bodies are generated automatically, by the recursive subdivision of a single Cartesian cell encompassing the entire flow domain. Where the resulting cells intersect bodies, polygonal cut cells are created using modified polygon-clipping algorithms. The grid is stored in a binary tree data structure that provides a natural means of obtaining cell-to-cell connectivity and of carrying out solution-adaptive mesh refinement. The Euler and Navier-Stokes equations are solved on the resulting grids using a finite volume formulation. The convective terms are upwinded: A linear reconstruction of the primitive variables is performed, providing input states to an approximate Riemann solver for computing the fluxes between neighboring cells. The results of a study comparing the accuracy and positivity of two classes of cell-centered, viscous gradient reconstruction procedures is briefly summarized. Adaptively refined solutions of the Navier-Stokes equations are shown using the more robust of these gradient reconstruction procedures, where the results computed by the Cartesian approach are compared to theory, experiment, and other accepted computational results for a series of low and moderate Reynolds number flows.
Kong, Ning; Jia, Shi-Rong; Tang, Qiao-Ling; Wang, Zhi-Xing
2014-01-01
The potential impact of transgene escape on the environment and food safety is a major concern to the scientists and public. This work aimed to assess the effect of intein-mediated gene splitting on containment of transgene flow. Two fusion genes, EPSPSn-In and Ic-EPSPSc, were constructed and integrated into N. tabacum, using Agrobacterium tumefaciens-mediated transformation. EPSPSn-In encodes the first 295 aa of the herbicide resistance gene 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) fused with the first 123 aa of the Ssp DnaE intein (In), whereas Ic-EPSPSc encodes the 36 C-terminal aa of the Ssp DnaE intein (Ic) fused to the rest of EPSPS C terminus peptide sequences. Both EPSPSn-In and Ic-EPSPSc constructs were introduced into the same N. tabacum genome by genetic crossing. Hybrids displayed resistance to the herbicide N-(phosphonomethyl)-glycine (glyphosate). Western blot analysis of protein extracts from hybrid plants identified full-length EPSPS. Furthermore, all hybrid seeds germinated and grew normally on glyphosate selective medium. The 6-8 leaf hybrid plants showed tolerance of 2000 ppm glyphosate in field spraying. These results indicated that functional EPSPS protein was reassembled in vivo by intein-mediated trans-splicing in 100% of plants. In order to evaluate the effect of the gene splitting technique for containment of transgene flow, backcrossing experiments were carried out between hybrids, in which the foreign genes EPSPSn-In and Ic-EPSPSc were inserted into different chromosomes, and non-transgenic plants NC89. Among the 2812 backcrossing progeny, about 25% (664 plantlets) displayed glyphosate resistance. These data indicated that transgene flow could be reduced by 75%. Overall, our findings provide a new and highly effective approach for biological containment of transgene flow. PMID:24915192
A Bayesian Hierarchical Modeling Approach to Predicting Flow in Ungauged Basins
NASA Astrophysics Data System (ADS)
Gronewold, A.; Alameddine, I.; Anderson, R. M.
2009-12-01
Recent innovative approaches to identifying and applying regression-based relationships between land use patterns (such as increasing impervious surface area and decreasing vegetative cover) and rainfall-runoff model parameters represent novel and promising improvements to predicting flow from ungauged basins. In particular, these approaches allow for predicting flows under uncertain and potentially variable future conditions due to rapid land cover changes, variable climate conditions, and other factors. Despite the broad range of literature on estimating rainfall-runoff model parameters, however, the absence of a robust set of modeling tools for identifying and quantifying uncertainties in (and correlation between) rainfall-runoff model parameters represents a significant gap in current hydrological modeling research. Here, we build upon a series of recent publications promoting novel Bayesian and probabilistic modeling strategies for quantifying rainfall-runoff model parameter estimation uncertainty. Our approach applies alternative measures of rainfall-runoff model parameter joint likelihood (including Nash-Sutcliffe efficiency, among others) to simulate samples from the joint parameter posterior probability density function. We then use these correlated samples as response variables in a Bayesian hierarchical model with land use coverage data as predictor variables in order to develop a robust land use-based tool for forecasting flow in ungauged basins while accounting for, and explicitly acknowledging, parameter estimation uncertainty. We apply this modeling strategy to low-relief coastal watersheds of Eastern North Carolina, an area representative of coastal resource waters throughout the world because of its sensitive embayments and because of the abundant (but currently threatened) natural resources it hosts. Consequently, this area is the subject of several ongoing studies and large-scale planning initiatives, including those conducted through the United
Simulation of axi-symmetric flow towards wells: A finite-difference approach
NASA Astrophysics Data System (ADS)
Louwyck, Andy; Vandenbohede, Alexander; Bakker, Mark; Lebbe, Luc
2012-07-01
A detailed finite-difference approach is presented for the simulation of transient radial flow in multi-layer systems. The proposed discretization scheme simulates drawdown within the well more accurately than commonly applied schemes. The solution is compared to existing (semi) analytical models for the simulation of slug tests and pumping tests with constant discharge in single- and multi-layer systems. For all cases, it is concluded that the finite-difference model approximates drawdown to acceptable accuracy. The main advantage of finite-difference approaches is the ability to account for the varying saturated thickness in unconfined top layers. Additionally, it is straightforward to include radial variation of hydraulic parameters, which is useful to simulate the effect of a finite-thickness well skin. Aquifer tests with variable pumping rate and/or multiple wells may be simulated by superposition. The finite-difference solution is implemented in MAxSym, a MATLAB tool which is designed specifically to simulate axi-symmetric flow. Alternatively, the presented equations can be solved using a standard finite-difference model. A procedure is outlined to apply the same approach with MODFLOW. The required modifications to the input parameters are much larger for MODFLOW than for MAxSym, but the results are virtually identical. The presented finite-difference solution may be used, for example, as a forward model in parameter estimation algorithms. Since it is applicable to multi-layer systems, its use is not limited to the simulation of traditional pumping and slug tests, but also includes advanced aquifer tests, such as multiple pumping tests or multi-level slug tests.
A dual-permeability approach to preferential water flow and solute transport in shrinking soils
NASA Astrophysics Data System (ADS)
Coppola, Antonio; dragonetti, giovanna; Comegna, Alessandro; Gerke, Horst H.; Basile, Angelo
2016-04-01
The pore systems in most natural soils is dynamically changing due to alternating swelling and shrinkage processes, which induces changes in pore volume and pore size distribution including deformations in pore geometry. This is a serious difficulty for modeling flow and transport in dual permeability approaches, as it will also require that the geometrical deformation of both the soil matrix and the fracture porous systems be taken into account, as well as the dynamics of soil hydraulic properties in response to the domain deformations. This study follows up a previous work by the same authors extending the classical rigid (RGD) approach formerly proposed by Gerke and van Genuchten, to account for shrinking effects (SHR) in modeling water flow and solute transport in dual-permeability porous media. In this study we considered three SHR scenarios, assuming that aggregate shrinkage may change either: (i) the hydraulic properties of the two pore domains, (ii) their relative fractions, and (iii) both, hydraulic properties and fractions of the two domains. The objective was to compare simulation results obtained under the RGD and the SHR assumptions to illustrate the impact of matrix volume changes on water storage, water fluxes and solute concentrations during: 1) An infiltration process bringing an initially dry soil to saturation, 2) A drainage process starting from an initially saturated soil. For an infiltration process, the simulated wetting front and the solute concentration propagation velocity, as well as the water fluxes, water and solute exchange rates, for the three SHR scenarios significantly deviated from the RGD. By contrast, relatively similar water content profiles evolved under all scenarios during drying. Overall, compared to the RGD approach, the effect of changing the hydraulic properties and the weight of the two domains according to the shrinkage behavior of the soil aggregates induced a much more rapid response in terms of water fluxes and
Cihan, Abdullah; Birkholzer, Jens; Trevisan, Luca; Bianchi, Marco; Zhou, Quanlin; Illangasekare, Tissa
2014-12-31
During CO_{2} injection and storage in deep reservoirs, the injected CO_{2} enters into an initially brine saturated porous medium, and after the injection stops, natural groundwater flow eventually displaces the injected mobile-phase CO_{2}, leaving behind residual non-wetting fluid. Accurate modeling of two-phase flow processes are needed for predicting fate and transport of injected CO_{2}, evaluating environmental risks and designing more effective storage schemes. The entrapped non-wetting fluid saturation is typically a function of the spatially varying maximum saturation at the end of injection. At the pore-scale, distribution of void sizes and connectivity of void space play a major role for the macroscopic hysteresis behavior and capillary entrapment of wetting and non-wetting fluids. This paper presents development of an approach based on the connectivity of void space for modeling hysteretic capillary pressure-saturation-relative permeability relationships. The new approach uses void-size distribution and a measure of void space connectivity to compute the hysteretic constitutive functions and to predict entrapped fluid phase saturations. Two functions, the drainage connectivity function and the wetting connectivity function, are introduced to characterize connectivity of fluids in void space during drainage and wetting processes. These functions can be estimated through pore-scale simulations in computer-generated porous media or from traditional experimental measurements of primary drainage and main wetting curves. The hysteresis model for saturation-capillary pressure is tested successfully by comparing the model-predicted residual saturation and scanning curves with actual data sets obtained from column experiments found in the literature. A numerical two-phase model simulator with the new hysteresis functions is tested against laboratory experiments conducted in a quasi-two-dimensional flow cell (91.4cm×5.6cm×61cm
Cihan, Abdullah; Birkholzer, Jens; Trevisan, Luca; ...
2014-12-31
During CO2 injection and storage in deep reservoirs, the injected CO2 enters into an initially brine saturated porous medium, and after the injection stops, natural groundwater flow eventually displaces the injected mobile-phase CO2, leaving behind residual non-wetting fluid. Accurate modeling of two-phase flow processes are needed for predicting fate and transport of injected CO2, evaluating environmental risks and designing more effective storage schemes. The entrapped non-wetting fluid saturation is typically a function of the spatially varying maximum saturation at the end of injection. At the pore-scale, distribution of void sizes and connectivity of void space play a major role formore » the macroscopic hysteresis behavior and capillary entrapment of wetting and non-wetting fluids. This paper presents development of an approach based on the connectivity of void space for modeling hysteretic capillary pressure-saturation-relative permeability relationships. The new approach uses void-size distribution and a measure of void space connectivity to compute the hysteretic constitutive functions and to predict entrapped fluid phase saturations. Two functions, the drainage connectivity function and the wetting connectivity function, are introduced to characterize connectivity of fluids in void space during drainage and wetting processes. These functions can be estimated through pore-scale simulations in computer-generated porous media or from traditional experimental measurements of primary drainage and main wetting curves. The hysteresis model for saturation-capillary pressure is tested successfully by comparing the model-predicted residual saturation and scanning curves with actual data sets obtained from column experiments found in the literature. A numerical two-phase model simulator with the new hysteresis functions is tested against laboratory experiments conducted in a quasi-two-dimensional flow cell (91.4cm×5.6cm×61cm), packed with homogeneous and
ERIC Educational Resources Information Center
Cermakova, Lucie; Moneta, Giovanni B.; Spada, Marcantonio M.
2010-01-01
This study investigated how attentional control and study-related dispositional flow influence students' approaches to studying when preparing for academic examinations. Based on information-processing theories, it was hypothesised that attentional control would be positively associated with deep and strategic approaches to studying, and…
An objective and parsimonious approach for classifying natural flow regimes at a continental scale
NASA Astrophysics Data System (ADS)
Archfield, S. A.; Kennen, J.; Carlisle, D.; Wolock, D.
2013-12-01
Hydroecological stream classification--the process of grouping streams by similar hydrologic responses and, thereby, similar aquatic habitat--has been widely accepted and is often one of the first steps towards developing ecological flow targets. Despite its importance, the last national classification of streamgauges was completed about 20 years ago. A new classification of 1,534 streamgauges in the contiguous United States is presented using a novel and parsimonious approach to understand similarity in ecological streamflow response. This new classification approach uses seven fundamental daily streamflow statistics (FDSS) rather than winnowing down an uncorrelated subset from 200 or more ecologically relevant streamflow statistics (ERSS) commonly used in hydroecological classification studies. The results of this investigation demonstrate that the distributions of 33 tested ERSS are consistently different among the classes derived from the seven FDSS. It is further shown that classification based solely on the 33 ERSS generally does a poorer job in grouping similar streamgauges than the classification based on the seven FDSS. This new classification approach has the additional advantages of overcoming some of the subjectivity associated with the selection of the classification variables and provides a set of robust continental-scale classes of US streamgauges.
An objective and parsimonious approach for classifying natural flow regimes at a continental scale
Archfield, Stacey A.; Kennen, Jonathan G.; Carlisle, Daren M.; Wolock, David M.
2014-01-01
Hydro-ecological stream classification-the process of grouping streams by similar hydrologic responses and, by extension, similar aquatic habitat-has been widely accepted and is considered by some to be one of the first steps towards developing ecological flow targets. A new classification of 1543 streamgauges in the contiguous USA is presented by use of a novel and parsimonious approach to understand similarity in ecological streamflow response. This novel classification approach uses seven fundamental daily streamflow statistics (FDSS) rather than winnowing down an uncorrelated subset from 200 or more ecologically relevant streamflow statistics (ERSS) commonly used in hydro-ecological classification studies. The results of this investigation demonstrate that the distributions of 33 tested ERSS are consistently different among the classification groups derived from the seven FDSS. It is further shown that classification based solely on the 33 ERSS generally does a poorer job in grouping similar streamgauges than the classification based on the seven FDSS. This new classification approach has the additional advantages of overcoming some of the subjectivity associated with the selection of the classification variables and provides a set of robust continental-scale classes of US streamgauges. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
Tardiole Kuehne, Bruno; Estrella, Julio Cezar; Nunes, Luiz Henrique; Martins de Oliveira, Edvard; Hideo Nakamura, Luis; Gomes Ferreira, Carlos Henrique; Carlucci Santana, Regina Helena; Reiff-Marganiec, Stephan; Santana, Marcos José
2015-01-01
This paper proposes a system named AWSCS (Automatic Web Service Composition System) to evaluate different approaches for automatic composition of Web services, based on QoS parameters that are measured at execution time. The AWSCS is a system to implement different approaches for automatic composition of Web services and also to execute the resulting flows from these approaches. Aiming at demonstrating the results of this paper, a scenario was developed, where empirical flows were built to demonstrate the operation of AWSCS, since algorithms for automatic composition are not readily available to test. The results allow us to study the behaviour of running composite Web services, when flows with the same functionality but different problem-solving strategies were compared. Furthermore, we observed that the influence of the load applied on the running system as the type of load submitted to the system is an important factor to define which approach for the Web service composition can achieve the best performance in production.
2013-01-01
Background The haemotropic mycoplasmas Mycoplasma haemofelis and Candidatus Mycoplasma haemominutum cause feline infectious anaemia with infection rates in feline populations reflecting widespread subclinical infection. Clinically significant infections are much rarer but can be life-threatening. Current diagnosis is dependent upon visualising organisms in stained blood smears, PCR or quantitative PCR (qPCR). These procedures are labour-intensive and time-consuming. Furthermore, PCR-based approaches offer limited insight into the disease burden of the infected animal. Methods We have developed a novel and rapid flow cytometric system that permits diagnosis of haemotropic mycoplasma infections and quantitation of the percentage of erythrocytes that are parasitized. The method exploits the fact that mature mammalian erythrocytes, the host cell for haemoplasmas, are enucleated and thus lack nucleic acid. DRAQ5 is a synthetic anthrocycline dye which rapidly crosses cell membranes and binds to nucleic acids. The presence of exogenous bacterial DNA in mammalian erythrocytes can, therefore, be detected by DRAQ5 uptake and flow cytometric detection of DRAQ5 fluorescence. Results Here, we show that this system can detect epi-erythrocytic infection of companion felines by haemotropic mycoplasma. Due to their differences in size, and hence the quantity of DNA, the two major feline hemoplasmas M. haemofelis and Candidatus M. haemominutum can be distinguished according to DRAQ5 fluorescence. We have also shown the usefulness of DRAQ5 uptake in monitoring a cat infected with M. haemofelis sequentially during treatment with doxycycline. Conclusions The technique described is the first report of a flow cytometric method for detecting haemotropic mycoplasmas in any species and could be applied to widespread screening of animal populations to assess infection by these epi-erythrocytic parasites. PMID:23725366
Ring resonator for biosensing via flow-through approach (Conference Presentation)
NASA Astrophysics Data System (ADS)
Bernini, Romeo; Grimaldi, Immacolata A.; Persichetti, Gianluca; Testa, Genni
2017-03-01
The realization of a simple real time biosensor, in which antibodies are immobilized onto surfaces, represents a promising application in the immunoassay development. Among the various sensing approaches, one of the most promising is based on microring resonators, offering a lot of advantages such as mass production, reduced dimensions, label-free and real time detection. The use of the evanescent field as optical transduction principle allows the development of label-free biosensors, in which the antibody is usually immobilized on the sensor surface and the binding of the antigen can be controlled and followed in real-time. The overall performances of immunosensors are strongly related to the optimization of the immobilization process and the integration between the microfluidic parts and the optical detection system. The combination of these two aspects makes the biosensing process very efficient, with a consequent reduction of the response time and improvement of the immobilization process efficiency. In this work we explore the working mechanism of a flow-through microresonator platform. A drilled hole, in the center of the ring, allows the active transport mechanism of the analyte toward the sensing surface with a consequent reduction of the response time. Moreover, we study the effects of oxygen plasma, in terms of duration times and plasma power, on immobilization efficiency of immunoglobulin G (IgG). An improvement of about 20% of the protein adsorption is ascribed to chemico-physical modification of SU-8. The measured sensor response time in flow-through configuration is about five times shorter respect to standard flow-over configuration.
NASA Astrophysics Data System (ADS)
Dagan, Gedeon; Rubin, Yoram
1988-10-01
In this paper, a stochastic method to identify aquifer natural recharge, storativity, and transmissivity under transient conditions is developed. Four main assumptions were adopted: Y, the log transmissivity, is a normal random space function, the aquifer is unbounded, a first-order approximation of the flow equation is adopted, and the transients are slowly varying. Based on these assumptions, the expected value of Y and of the head H, as well as their covariances and crosscovariances, are expressed by analytical equations which depend on a parameters vector θ. A major part of the first paper is devoted to the development of these expressions, based on the two-dimensional flow equation. The proposed solution of the inverse problem is a double-stage procedure. First, θ is identified stochastically, by a maximum likelihood procedure applied to the measurements of Y and H. Then, θ serves to estimate the spatial distributions of Y and H through their conditional mean and variances of estimation. The three main new features of the approach are the possibility to identify the spatial distributions of Y and H through their first two statistical moments based on transient head data and in the presence of pumping-recharching wells; the identification of the storativity and the stochastic identification of natural recharge. Since the proposed method make use of the analytic solution of the flow equation, it saves the need of laborious numerical schemes. Application of the method to a section of the Israeli Coastal Aquifer illustrates its potential in a real-life case.
Pina-Vaz, Cidália; Silva, Ana P.; Faria-Ramos, Isabel; Teixeira-Santos, Rita; Moura, Daniel; Vieira, Tatiana F.; Sousa, Sérgio F.; Costa-de-Oliveira, Sofia; Cantón, Rafael; Rodrigues, Acácio G.
2016-01-01
The synergy of carbapenem combinations regarding Enterobacteriaceae producing different types of carbapenemases was study through different approaches: flow cytometry and computational analysis. Ten well characterized Enterobacteriaceae (KPC, verona integron-encoded metallo-β-lactamases –VIM and OXA-48-like enzymes) were selected for the study. The cells were incubated with a combination of ertapenem with imipenem, meropenem, or doripenem and killing kinetic curves performed with and without reinforcements of the drugs. A cephalosporin was also used in combination with ertapenem. A flow cytometric assay with DiBAC4-(3), a membrane potential dye, was developed in order to evaluate the cellular lesion after 2 h incubation. A chemical computational study was performed to understand the affinity of the different drugs to the different types of enzymes. Flow cytometric analysis and time-kill assays showed a synergic effect against KPC and OXA-48 producing-bacteria with all combinations; only ertapenem with imipenem was synergic against VIM producing-bacteria. A bactericidal effect was observed in OXA-48-like enzymes. Ceftazidime plus ertapenem was synergic against ESBL-negative KPC producing-bacteria. Ertapenem had the highest affinity for those enzymes according to chemical computational study. The synergic effect between ertapenem and others carbapenems against different carbapenemase-producing bacteria, representing a therapeutic choice, was described for the first time. Easier and faster laboratorial methods for carbapenemase characterization are urgently needed. The design of an ertapenem derivative with similar affinity to carbapenemases but exhibiting more stable bonds was demonstrated as highly desirable. PMID:27555844
A hybrid FEM-DEM approach to the simulation of fluid flow laden with many particles
NASA Astrophysics Data System (ADS)
Casagrande, Marcus V. S.; Alves, José L. D.; Silva, Carlos E.; Alves, Fábio T.; Elias, Renato N.; Coutinho, Alvaro L. G. A.
2017-04-01
In this work we address a contribution to the study of particle laden fluid flows in scales smaller than TFM (two-fluid models). The hybrid model is based on a Lagrangian-Eulerian approach. A Lagrangian description is used for the particle system employing the discrete element method (DEM), while a fixed Eulerian mesh is used for the fluid phase modeled by the finite element method (FEM). The resulting coupled DEM-FEM model is integrated in time with a subcycling scheme. The aforementioned scheme is applied in the simulation of a seabed current to analyze which mechanisms lead to the emergence of bedload transport and sediment suspension, and also quantify the effective viscosity of the seabed in comparison with the ideal no-slip wall condition. A simulation of a salt plume falling in a fluid column is performed, comparing the main characteristics of the system with an experiment.
A minimally diffusive interface function steepening approach for compressible multiphase flows
NASA Astrophysics Data System (ADS)
Regele, Jonathan
2015-11-01
Interface capturing methods for contacts and shocks are commonly used in compressible multiphase flows. Artificial diffusion is inherently necessary to stabilize jump discontinuities across shocks and contacts. Contacts suffer from diffusion more severely than shock waves because their characteristics are not convergent like shocks. Interface steepening procedures are commonly used to counteract numerical diffusion necessary to maintain a sharp interface function. In this work, a modification to the sharpening approach used in Shukla, Pantano, and Freund [J. Comp. Phys, 229, 2010] is developed that minimizes the artificial diffusion across the interface while maintaining a monotonic interface function. The method requires fewer iterations for convergence and provides a steeper interface function. Examples in one and two dimensions demonstrate the method's performance.
NASA Astrophysics Data System (ADS)
Hung, P. C.; Irwin, G.; Kee, R.; McLoone, S.
2005-02-01
Thermocouples are one of the most popular devices for temperature measurement due to their robustness, ease of manufacture and installation, and low cost. However, when used in certain harsh environments, for example, in combustion systems and engine exhausts, large wire diameters are required, and consequently the measurement bandwidth is reduced. This article discusses a software compensation technique to address the loss of high frequency fluctuations based on measurements from two thermocouples. In particular, a difference equation (DE) approach is proposed and compared with existing methods both in simulation and on experimental test rig data with constant flow velocity. It is found that the DE algorithm, combined with the use of generalized total least squares for parameter identification, provides better performance in terms of time constant estimation without any a priori assumption on the time constant ratios of the thermocouples.
An acoustic-convective splitting-based approach for the Kapila two-phase flow model
NASA Astrophysics Data System (ADS)
ten Eikelder, M. F. P.; Daude, F.; Koren, B.; Tijsseling, A. S.
2017-02-01
In this paper we propose a new acoustic-convective splitting-based numerical scheme for the Kapila five-equation two-phase flow model. The splitting operator decouples the acoustic waves and convective waves. The resulting two submodels are alternately numerically solved to approximate the solution of the entire model. The Lagrangian form of the acoustic submodel is numerically solved using an HLLC-type Riemann solver whereas the convective part is approximated with an upwind scheme. The result is a simple method which allows for a general equation of state. Numerical computations are performed for standard two-phase shock tube problems. A comparison is made with a non-splitting approach. The results are in good agreement with reference results and exact solutions.
NASA Technical Reports Server (NTRS)
Egolf, T. A.; Landgrebe, A. J.
1982-01-01
A user's manual is provided which includes the technical approach for the Prescribed Wake Rotor Inflow and Flow Field Prediction Analysis. The analysis is used to provide the rotor wake induced velocities at the rotor blades for use in blade airloads and response analyses and to provide induced velocities at arbitrary field points such as at a tail surface. This analysis calculates the distribution of rotor wake induced velocities based on a prescribed wake model. Section operating conditions are prescribed from blade motion and controls determined by a separate blade response analysis. The analysis represents each blade by a segmented lifting line, and the rotor wake by discrete segmented trailing vortex filaments. Blade loading and circulation distributions are calculated based on blade element strip theory including the local induced velocity predicted by the numerical integration of the Biot-Savart Law applied to the vortex wake model.
An optimization approach for large scale simulations of discrete fracture network flows
NASA Astrophysics Data System (ADS)
Berrone, Stefano; Pieraccini, Sandra; Scialò, Stefano
2014-01-01
In recent papers [1,2] the authors introduced a new method for simulating subsurface flow in a system of fractures based on a PDE-constrained optimization reformulation, removing all difficulties related to mesh generation and providing an easily parallel approach to the problem. In this paper we further improve the method removing the constraint of having on each fracture a non-empty portion of the boundary with Dirichlet boundary conditions. This way, Dirichlet boundary conditions are prescribed only on a possibly small portion of DFN boundary. The proposed generalization of the method in [1,2] relies on a modified definition of control variables ensuring the non-singularity of the operator on each fracture. A conjugate gradient method is also introduced in order to speed up the minimization process.
A triple-continuum approach for modeling flow and transportprocesses in fractured rock
Wu, Yu-Shu; Liu, H.H.; Bodvarsson, G.S; Zellmer, K .E.
2001-08-31
This paper presents a triple-continuum conceptual model forsimulating flow and transport processes in fractured rock. Field datacollected from the unsaturated zone of Yucca Mountain, a repository siteof high-level nuclear waste, show a large number of small-scalefractures. The effect of these small fractures has not been considered inprevious modeling investigations within the context of a continuumapproach. A new triple-continuum model (consisting of matrix,small-fracture, and large-fracture continua) has been developed toinvestigate the effect of these small fractures. This paper derives themodel formulation and discusses the basic triple-continuum behavior offlow and transport processes under different conditions, using bothanalytical solutions and numerical approaches. The simulation resultsfrom the site-scale model of the unsaturated zone of Yucca Mountainindicate that these small fractures may have an important effect onradionuclide transport within the mountain
NASA Astrophysics Data System (ADS)
Dhiman, S. K.; Prasad, J. K.; Kumar, Arbind
2017-05-01
Series of experiments were conducted in order to develop empirical correlations to predict average Nusselt number on different segments of each of the two tandem cylinders and the overall average Nusselt number for unsteady state heat transfer in cross flow of air past tandem cylinders under constant heat flux supply condition. The unsteady-state Nusselt number distributions over the cylinders surface were determined using inverse heat conduction approach. During experimentation, the center-to-center spacing between the cylinders was varied from 1.2 to 4.0 times the cylinder diameter and that the Reynolds number from 1.1 × 104 to 6.2 × 104. The air was allowed to flow past the tandem cylinders for few fraction of a second only. A curve of constant C was plotted as a function of spacing ratio, which was used in the empirical correlation to determine overall average Nusselt number. The mean deviation of overall average Nusselt number predicted from the developed correlation was found within ±2.9% from the experimental values. From the results of average Nusselt number, the maximum heat transfer condition was obtained at spacing ratio of 2.2.
Warid, Warid; Hizam, Hashim; Mariun, Norman; Abdul-Wahab, Noor Izzri
2016-01-01
This paper proposes a new formulation for the multi-objective optimal power flow (MOOPF) problem for meshed power networks considering distributed generation. An efficacious multi-objective fuzzy linear programming optimization (MFLP) algorithm is proposed to solve the aforementioned problem with and without considering the distributed generation (DG) effect. A variant combination of objectives is considered for simultaneous optimization, including power loss, voltage stability, and shunt capacitors MVAR reserve. Fuzzy membership functions for these objectives are designed with extreme targets, whereas the inequality constraints are treated as hard constraints. The multi-objective fuzzy optimal power flow (OPF) formulation was converted into a crisp OPF in a successive linear programming (SLP) framework and solved using an efficient interior point method (IPM). To test the efficacy of the proposed approach, simulations are performed on the IEEE 30-busand IEEE 118-bus test systems. The MFLP optimization is solved for several optimization cases. The obtained results are compared with those presented in the literature. A unique solution with a high satisfaction for the assigned targets is gained. Results demonstrate the effectiveness of the proposed MFLP technique in terms of solution optimality and rapid convergence. Moreover, the results indicate that using the optimal DG location with the MFLP algorithm provides the solution with the highest quality.
Warid, Warid; Hizam, Hashim; Mariun, Norman; Abdul-Wahab, Noor Izzri
2016-01-01
This paper proposes a new formulation for the multi-objective optimal power flow (MOOPF) problem for meshed power networks considering distributed generation. An efficacious multi-objective fuzzy linear programming optimization (MFLP) algorithm is proposed to solve the aforementioned problem with and without considering the distributed generation (DG) effect. A variant combination of objectives is considered for simultaneous optimization, including power loss, voltage stability, and shunt capacitors MVAR reserve. Fuzzy membership functions for these objectives are designed with extreme targets, whereas the inequality constraints are treated as hard constraints. The multi-objective fuzzy optimal power flow (OPF) formulation was converted into a crisp OPF in a successive linear programming (SLP) framework and solved using an efficient interior point method (IPM). To test the efficacy of the proposed approach, simulations are performed on the IEEE 30-busand IEEE 118-bus test systems. The MFLP optimization is solved for several optimization cases. The obtained results are compared with those presented in the literature. A unique solution with a high satisfaction for the assigned targets is gained. Results demonstrate the effectiveness of the proposed MFLP technique in terms of solution optimality and rapid convergence. Moreover, the results indicate that using the optimal DG location with the MFLP algorithm provides the solution with the highest quality. PMID:26954783
Ghosh, Sayari; Chakraborty, Ishita; Chakraborty, Monojit; Mukhopadhyay, Ashis; Mishra, Raghwendra; Sarkar, Debasish
2016-04-01
Erythrocyte morphology is gaining importance as a powerful pathological index in identifying the severity of any blood related disease. However, the existing technique of quantitative microscopy is highly time consuming and prone to personalized bias. On the other hand, relatively unexplored, complementary technique based on flow cytometry has not been standardized till date, particularly due to the lack of a proper morphological scoring scale. In this article, we have presented a new approach to formulate a non-empirical scoring scale based on membrane roughness (R(rms)) data obtained from atomic force microscopy. Subsequently, the respective morphological quantifier of the whole erythrocyte population, commonly known as morphological index, was expressed as a function of highest correlated statistical parameters of scattered signal profiles generated by flow cytometry. Feed forward artificial neural network model with multilayer perceptron architecture was used to develop the intended functional form. High correlation coefficient (R(2) = 0.95), even for model-formulation exclusive samples, clearly indicates the universal validity of the proposed model. Moreover, a direct pathological application of the proposed model has been illustrated in relation to patients, diagnosed to be suffering from a wide variety of cancer.
An Integrated Design approach to Power Systems: from Power Flows to Electricity Markets
NASA Astrophysics Data System (ADS)
Bose, Subhonmesh
Power system is at the brink of change. Engineering needs, economic forces and environmental factors are the main drivers of this change. The vision is to build a smart electrical grid and a smarter market mechanism around it to fulfill mandates on clean energy. Looking at engineering and economic issues in isolation is no longer an option today; it needs an integrated design approach. In this thesis, I shall revisit some of the classical questions on the engineering operation of power systems that deals with the nonconvexity of power flow equations. Then I shall explore some issues of the interaction of these power flow equations on the electricity markets to address the fundamental issue of market power in a deregulated market environment. Finally, motivated by the emergence of new storage technologies, I present an interesting result on the investment decision problem of placing storage over a power network. The goal of this study is to demonstrate that modern optimization and game theory can provide unique insights into this complex system. Some of the ideas carry over to applications beyond power systems.
Fluid migration in the subduction zone: a coupled fluid flow approach
NASA Astrophysics Data System (ADS)
Wang, Hongliang; Huismans, Ritske; Rondenay, Stéphane
2016-04-01
Subduction zone are the main entry point of water into earth's mantle and play an important role in the global water cycle. The progressive release of water by metamorphic dehydration induce important physical-chemical process in the subduction zone, such as hydrous melting, hydration and weakening of the mantle wedge, creation of pore fluid pressures that may weaken the subduction interface and induce earthquakes. Most previous studies on the role of fluids in subduction zones assume vertical migration or migration according to the dynamic pressure in the solid matrix without considering the pore fluid pressure effect on the deformation of the solid matrix. Here we investigate this interaction by explicitly modeling two-phase coupled poro-plastic flow during subduction. In this approach, the fluid migrates by compaction and decompaction of the solid matrix and affects the subduction dynamics through pore fluid pressure dependent frictional-plastic yield. Our preliminary results indicate that: 1) the rate of fluid migration depends strongly on the permeability and the bulk viscosity of the solid matrix, 2) fluid transfer occurs preferentially along the slab and then propagates into the mantle wedge by viscous compaction driven fluid flow, 3) fluid transport from the surface to depth is a prerequisite for producing high fluid pore pressures and associated hydration induced weakening of the subduction zone interface.
Bailey, Matthew R; Pentecost, Amber M; Selimovic, Asmira; Martin, R Scott; Schultz, Zachary D
2015-04-21
The combination of hydrodynamic focusing with embedded capillaries in a microfluidic device is shown to enable both surface enhanced Raman scattering (SERS) and electrochemical characterization of analytes at nanomolar concentrations in flow. The approach utilizes a versatile polystyrene device that contains an encapsulated microelectrode and fluidic tubing, which is shown to enable straightforward hydrodynamic focusing onto the electrode surface to improve detection. A polydimethyslsiloxane (PDMS) microchannel positioned over both the embedded tubing and SERS active electrode (aligned ∼200 μm from each other) generates a sheath flow that confines the analyte molecules eluting from the embedded tubing over the SERS electrode, increasing the interaction between the Riboflavin (vitamin B2) and the SERS active electrode. The microfluidic device was characterized using finite element simulations, amperometry, and Raman experiments. This device shows a SERS and amperometric detection limit near 1 and 100 nM, respectively. This combination of SERS and amperometry in a single device provides an improved method to identify and quantify electroactive analytes over either technique independently.
Engineering approach to the prediction of shock patterns in bounded high-speed flows
NASA Technical Reports Server (NTRS)
Azevedo, D. J.; Liu, Ching Shi
1993-01-01
A two-dimensional symmetric wedge configuration representative of a single high-speed intake in steady flow was investigated. The analysis presented here is intended as an engineering approach for estimating certain features of the internal shock system. The primary interest here is the prediction of the size and location of the almost-normal shock wave that develops when the leading-edge shocks intersect at angles above a certain critical value that is less than the wedge detachment angle. The almost-normal shock wave is frequently referred to as the 'Mach stem', Parametric studies enabled the sensitivity of the Mach stem height to various flowfield parameters to be examined, thus indicating how accurately these parameters must be measured in a given experiment. Results of these predictions were compared with those of a steady-flow experiment performed at nominal freestream Mach numbers from 2.8 to 5. The predicted stem heights were consistently lower than the mean experimental values, attributable both to experimental uncertainties and to certain simplifying assumptions used in the analysis. Modification of these assumptions to better represent the test environment improved the analytical results.
A multiscale approach to study the stability of long waves in near-parallel flows
NASA Astrophysics Data System (ADS)
Scarsoglio, Stefania; Tordella, Daniela; Criminale, William
2007-11-01
The linear stability of a two-dimensional non-parallel flow is considered as an initial-value problem. A spatio-temporal multiscale approach is assumed. The choice of the polar wavenumber (k->0) as the small parameter (Blossey, Criminale & Fisher 2007) leads to a regular perturbation scheme. The introduction, in the perturbation Fourier decomposition, of a complex longitudinal wavenumber (Scarsoglio, Tordella & Criminale 2007) makes the problem well-posed at any order. By imposing arbitrary three-dimensional disturbances in terms of the vorticity, both the early transient as well as the asymptotic fate can be observed (Criminale & Drazin 1990). An example concerning the stability of a growing wake is presented (basic flow as U(x,y), V(x,y), Tordella & Belan 2003). A summary of significant early time transients is shown. In the longitudinal perturbation case, asymptotic temporal results are compared with multiscale normal mode analyses (small parameter 1/R) for the intermediate and far wake (Tordella, Scarsoglio & Belan 2006; Belan & Tordella 2006).
Engineering approach to the prediction of shock patterns in bounded high-speed flows
NASA Technical Reports Server (NTRS)
Azevedo, D. J.; Liu, Ching Shi
1993-01-01
A two-dimensional symmetric wedge configuration representative of a single high-speed intake in steady flow was investigated. The analysis presented here is intended as an engineering approach for estimating certain features of the internal shock system. The primary interest here is the prediction of the size and location of the almost-normal shock wave that develops when the leading-edge shocks intersect at angles above a certain critical value that is less than the wedge detachment angle. The almost-normal shock wave is frequently referred to as the 'Mach stem', Parametric studies enabled the sensitivity of the Mach stem height to various flowfield parameters to be examined, thus indicating how accurately these parameters must be measured in a given experiment. Results of these predictions were compared with those of a steady-flow experiment performed at nominal freestream Mach numbers from 2.8 to 5. The predicted stem heights were consistently lower than the mean experimental values, attributable both to experimental uncertainties and to certain simplifying assumptions used in the analysis. Modification of these assumptions to better represent the test environment improved the analytical results.
Modern approaches to processing large hyperspectral and multispectral aerospace data flows
NASA Astrophysics Data System (ADS)
Bondur, V. G.
2014-12-01
We consider approaches to processing large hyperspectral and multispectral imaging flows produced in aerospace monitoring for solving a wide range of problems of management of natural resources, environmental security, prevention of natural disasters and technogenic accidents, as well as problems of real economy, and basic and applied sciences. We analyze the specific features of the phases of hyperspectral data analysis and describe a software and hardware system that uses new and improved methods and algorithms for processing large flows of hyperspectral and other aerospace data and has a high-performance computer. This system contains different types of software for identifying the types of given objects by solving inverse problems of remote sensing as well as by analyzing their qualitative and quantitative characteristics, combined multiparameter processing of hyperspectral aerospace data, tracking the local changes including those related to changes in meteorological conditions and vegetation periods, detecting and identifying the types of small objects on the basis of analysis of individual parts of the image, detecting and identifying heat sources, etc. We bring examples of processing of hyperspectral and multispectral satellite images with the help of software and hardware tools developed.
NASA Astrophysics Data System (ADS)
Liu, Shun; Xu, Jinglei; Yu, Kaikai
2017-06-01
This paper proposes an improved approach for extraction of pressure fields from velocity data, such as obtained by particle image velocimetry (PIV), especially for steady compressible flows with strong shocks. The principle of this approach is derived from Navier-Stokes equations, assuming adiabatic condition and neglecting viscosity of flow field boundaries measured by PIV. The computing method is based on MacCormack's technique in computational fluid dynamics. Thus, this approach is called the MacCormack method. Moreover, the MacCormack method is compared with several approaches proposed in previous literature, including the isentropic method, the spatial integration and the Poisson method. The effects of velocity error level and PIV spatial resolution on these approaches are also quantified by using artificial velocity data containing shock waves. The results demonstrate that the MacCormack method has higher reconstruction accuracy than other approaches, and its advantages become more remarkable with shock strengthening. Furthermore, the performance of the MacCormack method is also validated by using synthetic PIV images with an oblique shock wave, confirming the feasibility and advantage of this approach in real PIV experiments. This work is highly significant for the studies on aerospace engineering, especially the outer flow fields of supersonic aircraft and the internal flow fields of ramjets.
NASA Astrophysics Data System (ADS)
Nezlobin, David; Pariente, Sarah; Lavee, Hanoch; Sachs, Eyal
2017-04-01
Source-sink systems are very common in hydrology; in particular, some land cover types often generate runoff (e.g. embedded rocks, bare soil) , while other obstruct it (e.g. vegetation, cracked soil). Surface runoff coefficients of patchy slopes/plots covered by runoff generating and obstructing covers (e.g., bare soil and vegetation) depend critically on the percentage cover (i.e. sources/sinks abundance) and decrease strongly with observation scale. The classic mathematical percolation theory provides a powerful apparatus for describing the runoff connectivity on patchy hillslopes, but it ignores strong effect of the overland flow directionality. To overcome this and other difficulties, modified percolation theory approaches can be considered, such as straight percolation (for the planar slopes), quasi-straight percolation and models with limited obstruction. These approaches may explain both the observed critical dependence of runoff coefficients on percentage cover and their scale decrease in systems with strong flow directionality (e.g. planar slopes). The contributing area increases sharply when the runoff generating percentage cover approaches the straight percolation threshold. This explains the strong increase of the surface runoff and erosion for relatively low values (normally less than 35%) of the obstructing cover (e.g., vegetation). Combinatorial models of urns with restricted occupancy can be applied for the analytic evaluation of meaningful straight percolation quantities, such as NOGA's (Non-Obstructed Generating Area) expected value and straight percolation probability. It is shown that the nature of the cover-related runoff scale decrease is combinatorial - the probability for the generated runoff to avoid obstruction in unit area decreases with scale for the non-trivial percentage cover values. The magnitude of the scale effect is found to be a skewed non-monotonous function of the percentage cover. It is shown that the cover-related scale
Inverse modeling of dynamic nonequilibrium in water flow with an effective approach
NASA Astrophysics Data System (ADS)
Diamantopoulos, E.; Iden, S. C.; Durner, W.
2012-03-01
Observations of water flow in unsaturated soils often show "dynamic effects," indicated by nonequilibrium between water contents and water potential, a phenomenon that cannot be modeled with the Richards equation. The objective of this article is to formulate an effective process description of dynamic nonequilibrium flow in variably saturated soil which is both flexible enough to match experimental observations and as parsimonious as possible to allow unique parameter estimation by inverse modeling. In the conceptual model, water content is partitioned into two fractions. Water in one fraction is in equilibrium with the pressure head, whereas water in the second fraction is in nonequilibrium, described by the kinetic equilibration approach of Ross and Smettem (2000). Between the two fractions an instantaneous equilibration of the pressure head is assumed. The new model, termed the dual-fraction nonequilibrium model, requires only one additional parameter compared to the nonequilibrium approach of Ross and Smettem. We tested the model with experimental data from multistep outflow experiments conducted on two soils and compared it to the Richards equation, the nonequilibrium model of Ross and Smettem, and the dual-porosity model of Philip (1968). The experimental data were evaluated by inverse modeling using a robust Markov chain Monte Carlo sampler. The results show that the proposed model is superior to the Richards equation and the Ross and Smettem model in describing dynamic nonequilibrium effects occurring in multistep outflow experiments. The three popular model selection criteria (Akaike information criterion, Bayesian information criterion, and deviance information criterion) all favored the new model because of its smaller number of parameters.
NASA Astrophysics Data System (ADS)
Gubchenko, V. M.
2015-12-01
The formation of magnetic structures in moving hot solar coronal plasma and hot collisionless laser-produced plasma, as determined by nonlinear criteria for weak and strong magnetization on the basis of the friction parameter Γ B and Alfven number M A, is considered within the Vlasov and Maxwell equations in the second part of the work. The flow velocities are lower then the thermal electron velocity. The energy and pulse anisotropy parameters of a flow, which determine its electromagnetic properties in the Cherenkov resonance line, are calculated by shape of particle distribution function (PDF). The ratio of these parameters is the Q-factor G V ; it characterizes the electromagnetic properties of a plasma flow and is expressed via the ratio of diamagnetic and resistive current densities or via the ratio of irregular and diamagnetic plasma scales. A particle flow is similar to a conductive medium at G V ≪ 1 and a diamagnetic medium at G V ≫ 1. The following cases are considered. (1) A plasma flow is specified by an isotropic PDF and interacts with distributed magnetization. Expressions for anisotropy parameters are derived, 3D field structures in the tail wake are found, and a possibility of topological reconstruction into a compact state under variation in the parameter G V is shown. (2) A plasma flow is specified by an isotropic PDF; a steady-state diamagnetic current layer, characterized by an anisotropic PDF, is immersed inside it. The system is in the diamagnetic state G ≫ 1. The generalized anisotropy parameter is calculated and a possibility of the excitation of three types of diamagnetic structures with low resistive currents is shown. (3) The nonlinear dynamics of anisotropic quasi-current-free plasma ( G =-1), in which the diamagnetic and resistive current densities locally compensate each other in the phase space of particle velocities, is studied. This dynamics is implemented in the long wavelength limit in plasma with an anisotropic PDF.
Discrepancies between two measurements and two model approaches for liquid water flow in snow
NASA Astrophysics Data System (ADS)
Wever, N.; Schmid, L.; Heilig, A.; Fierz, C. G.; Lehning, M.
2014-12-01
Liquid water flow in snowpacks is a complicated process to measure or to simulate in snowpack models, although it is important for assessing, for example, soil moisture variations, streamflow discharge or wet snow avalanche formation. The measurement site Weissfluhjoch (WFJ) is equipped with instruments recording meteorological conditions and snowpack properties, including a snow lysimeter and an upward looking ground penetrating radar (upGPR). The upGRP, among other capabilities, is able to track the progress of the melt water front through the seasonal snowpack at WFJ, whereas the snow lysimeter only records liquid water runoff from the snowpack. The 1 dimensional physics-based snowpack model SNOWPACK has recently been extended with a solver for Richards equation, which provides a demonstrable improvement in simulating snowpack runoff, especially on the hourly time scale, when compared to a simpler bucket-type approach. Here, we compare the two measurement methods and the two snowpack simulations for four snow seasons with respect to the progress of the melt water front through the snowpack and snowpack runoff. We show that in the studied period, snowpack runoff in the melt season starts before the arrival of the melt water front at the bottom of the snowpack as detected by the upGPR. This discrepancy is in the order of several days to 1-2 weeks. The agreement between measured and modeled snowpack runoff is higher, although modeled snowpack runoff is still lagging several days from observed runoff, depending on the used water transport scheme. This demonstrates that the early start of snowpack runoff is likely associated with the existence of preferential flow paths. The modeled progress of the melt water front is faster than observed in the upGPR data. This contributes to a better predicition of the onset of snowpack runoff, but may have consequences for the representation of the internal snowpack in the model. The study highlights the extreme difficulties in
ERIC Educational Resources Information Center
Gaske, Dan
1992-01-01
Provides a graphical framework for presenting interactions among current account flows, capital account flows, and exchange rates. Suggests that the two type of flows must be considered separately in discussions of foreign exchange equilibrium and balance of payments flows. Supplies sample graphs and instructions for applying the framework to real…
ERIC Educational Resources Information Center
Gaske, Dan
1992-01-01
Provides a graphical framework for presenting interactions among current account flows, capital account flows, and exchange rates. Suggests that the two type of flows must be considered separately in discussions of foreign exchange equilibrium and balance of payments flows. Supplies sample graphs and instructions for applying the framework to real…
Kuniansky, Eve L.
2016-09-22
been developed that incorporate the submerged conduits as a one-dimensional pipe network within the aquifer rather than as discrete, extremely transmissive features in a porous-equivalent medium; these submerged conduit models are usually referred to as hybrid models and may include the capability to simulate both laminar and turbulent flow in the one-dimensional pipe network. Comparisons of the application of a porous-equivalent media model with and without turbulence (MODFLOW-Conduit Flow Process mode 2 and basic MODFLOW, respectively) and a hybrid (MODFLOW-Conduit Flow Process mode 1) model to the Woodville Karst Plain near Tallahassee, Florida, indicated that for annual, monthly, or seasonal average hydrologic conditions, all methods met calibration criteria (matched observed groundwater levels and average flows). Thus, the increased effort required, such as the collection of data on conduit location, to develop a hybrid model and its increased computational burden, is not necessary for simulation of average hydrologic conditions (non-laminar flow effects on simulated head and spring discharge were minimal). However, simulation of a large storm event in the Woodville Karst Plain with daily stress periods indicated that turbulence is important for matching daily springflow hydrographs. Thus, if matching streamflow hydrographs over a storm event is required, the simulation of non-laminar flow and the location of conduits are required. The main challenge in application of the methods and approaches for developing hybrid models relates to the difficulty of mapping conduit networks or having high-quality datasets to calibrate these models. Additionally, hybrid models have long simulation times, which can preclude the use of parameter estimation for calibration. Simulation of contaminant transport that does not account for preferential flow through conduits or extremely permeable zones in any approach is ill-advised. Simulation results in other karst aquifers or other
Large Scale Debris-flow Hazard Assessment : A Geotechnical Approach and Gis Modelling
NASA Astrophysics Data System (ADS)
Delmonaco, G.; Leoni, G.; Margottini, C.; Puglisi, C.; Spizzichino, D.
A deterministic approach has been developed for large-scale landslide hazard analysis carried out by ENEA, the Italian Agency for New Technologies, Energy and Environ- ment, in the framework of TEMRAP- The European Multi-Hazard Risk Assessment Project, finalised to the application of methodologies to incorporate the reduction of natural disasters. The territory of Versilia, and in particular the basin of Vezza river (60 Km2), has been chosen as test area of the project. The Vezza river basin, was affected by over 250 shallow landslides (debris/earth flow) mainly involving the metamorphic geological formations outcropping in the area triggered by the hydro-meteorological event of 19th June 1996. Many approaches and methodologies have been proposed in the scientific literature aimed at assessing landslide hazard and risk, depending es- sentially on scope of work, availability of data and scale of representation. In the last decades landslide hazard and risk analyses have been favoured by the development of GIS techniques that have permitted to generalise, synthesise and model the stability conditions at large scale (>1:10.000) investigation. In this work, the main results de- rived by the application of a geotechnical model coupled with a hydrological model for the assessment of debris flows hazard analysis, are reported. The deterministic analysis has been developed through the following steps: 1) elaboration of a landslide inventory map through aerial photo interpretation and direct field survey; 2) genera- tion of a data-base and digital maps; 3) elaboration of a DTM and slope angle map; 4) definition of a superficial soil thickness map; 5) litho-technical soil characterisation, through implementation of a back-analysis on test slopes and laboratory test analy- sis; 6) inference of the influence of precipitation, for distinct return times, on ponding time and pore pressure generation; 7) implementation of a slope stability model (in- finite slope model) and
NASA Astrophysics Data System (ADS)
Gallant, E.; Connor, C.; Richardson, J. A.; Wetmore, P. H.; Connor, L.
2015-12-01
We present the results of a lava flow hazard assessment for the Idaho National Laboratory (INL) using a new lava flow code, MOLASSES (MOdular LAva Simulation Software for Earth Science). INL is a nuclear research and development facility located on the eastern Snake River Plain with the potential for lava flow inundation from both monogenetic and polygenetic basaltic eruptions. Previously published inventories of observed surface vents and vents that are buried by younger lava flows and inferred from interpretation of borehole stratigraphy were used to created spatial density maps of vents within the INL region. Monte carlo simulations were run using the MOLASSES code to compare the difference between events initiated using only surface vents and events initiated using both the surface and the buried vents. We find that the inclusion of the buried vent locations drastically increases the number of site inundations and events initiating within INL boundaries. This highlights the need to seek out a more complete eruption record in an area of heavy prehistoric activity to better assess future hazard and associated risk.
Comparison of two different approaches for the control of convectively unstable flows
NASA Astrophysics Data System (ADS)
Juillet, Fabien; Schmid, Peter; McKeon, Beverley; Huerre, Patrick
2011-11-01
The probably most widely used control strategy in the literature is based on the Linear Quadratic Gaussian (LQG) framework. However, this approach seems to be difficult to apply to some fluid systems. In particular, due to their high sensitivity to external noise, amplifier flows are hard to control and the classical LQG compensator may be unable to describe the noise with sufficient accuracy. Another strategy aims at directly measuring these noise sources through a sensor called ``spy.'' The LQG and the spy approaches will be presented and compared using the Ginzburg-Landau equation as a model. It will be shown that the use of a spy is particularly relevant for convectively unstable systems. In addition, the ability of Subspace Identification Methods to provide satisfactory models is demonstrated. Finally, the findings from the Ginzburg-Landau investigation are generalized and applied to a more realistic system, namely a backward-facing step at Re = 350 . Support from Ecole Polytechnique and the Partner University Fund (PUF) is gratefully acknowledged.
A robust approach to chance constrained optimal power flow with renewable generation
Lubin, Miles; Dvorkin, Yury; Backhaus, Scott N.
2016-09-01
Optimal Power Flow (OPF) dispatches controllable generation at minimum cost subject to operational constraints on generation and transmission assets. The uncertainty and variability of intermittent renewable generation is challenging current deterministic OPF approaches. Recent formulations of OPF use chance constraints to limit the risk from renewable generation uncertainty, however, these new approaches typically assume the probability distributions which characterize the uncertainty and variability are known exactly. We formulate a robust chance constrained (RCC) OPF that accounts for uncertainty in the parameters of these probability distributions by allowing them to be within an uncertainty set. The RCC OPF is solved using a cutting-plane algorithm that scales to large power systems. We demonstrate the RRC OPF on a modified model of the Bonneville Power Administration network, which includes 2209 buses and 176 controllable generators. In conclusion, deterministic, chance constrained (CC), and RCC OPF formulations are compared using several metrics including cost of generation, area control error, ramping of controllable generators, and occurrence of transmission line overloads as well as the respective computational performance.
A robust approach to chance constrained optimal power flow with renewable generation
Lubin, Miles; Dvorkin, Yury; Backhaus, Scott N.
2016-09-01
Optimal Power Flow (OPF) dispatches controllable generation at minimum cost subject to operational constraints on generation and transmission assets. The uncertainty and variability of intermittent renewable generation is challenging current deterministic OPF approaches. Recent formulations of OPF use chance constraints to limit the risk from renewable generation uncertainty, however, these new approaches typically assume the probability distributions which characterize the uncertainty and variability are known exactly. We formulate a robust chance constrained (RCC) OPF that accounts for uncertainty in the parameters of these probability distributions by allowing them to be within an uncertainty set. The RCC OPF is solved usingmore » a cutting-plane algorithm that scales to large power systems. We demonstrate the RRC OPF on a modified model of the Bonneville Power Administration network, which includes 2209 buses and 176 controllable generators. In conclusion, deterministic, chance constrained (CC), and RCC OPF formulations are compared using several metrics including cost of generation, area control error, ramping of controllable generators, and occurrence of transmission line overloads as well as the respective computational performance.« less
A robust approach to chance constrained optimal power flow with renewable generation
Lubin, Miles; Dvorkin, Yury; Backhaus, Scott N.
2016-09-01
Optimal Power Flow (OPF) dispatches controllable generation at minimum cost subject to operational constraints on generation and transmission assets. The uncertainty and variability of intermittent renewable generation is challenging current deterministic OPF approaches. Recent formulations of OPF use chance constraints to limit the risk from renewable generation uncertainty, however, these new approaches typically assume the probability distributions which characterize the uncertainty and variability are known exactly. We formulate a robust chance constrained (RCC) OPF that accounts for uncertainty in the parameters of these probability distributions by allowing them to be within an uncertainty set. The RCC OPF is solved using a cutting-plane algorithm that scales to large power systems. We demonstrate the RRC OPF on a modified model of the Bonneville Power Administration network, which includes 2209 buses and 176 controllable generators. In conclusion, deterministic, chance constrained (CC), and RCC OPF formulations are compared using several metrics including cost of generation, area control error, ramping of controllable generators, and occurrence of transmission line overloads as well as the respective computational performance.
Zhang, Xuejun; Lei, Jiaxing
2015-01-01
Considering reducing the airspace congestion and the flight delay simultaneously, this paper formulates the airway network flow assignment (ANFA) problem as a multiobjective optimization model and presents a new multiobjective optimization framework to solve it. Firstly, an effective multi-island parallel evolution algorithm with multiple evolution populations is employed to improve the optimization capability. Secondly, the nondominated sorting genetic algorithm II is applied for each population. In addition, a cooperative coevolution algorithm is adapted to divide the ANFA problem into several low-dimensional biobjective optimization problems which are easier to deal with. Finally, in order to maintain the diversity of solutions and to avoid prematurity, a dynamic adjustment operator based on solution congestion degree is specifically designed for the ANFA problem. Simulation results using the real traffic data from China air route network and daily flight plans demonstrate that the proposed approach can improve the solution quality effectively, showing superiority to the existing approaches such as the multiobjective genetic algorithm, the well-known multiobjective evolutionary algorithm based on decomposition, and a cooperative coevolution multiobjective algorithm as well as other parallel evolution algorithms with different migration topology. PMID:26180840
Estimating construction and demolition debris generation using a materials flow analysis approach.
Cochran, K M; Townsend, T G
2010-11-01
The magnitude and composition of a region's construction and demolition (C&D) debris should be understood when developing rules, policies and strategies for managing this segment of the solid waste stream. In the US, several national estimates have been conducted using a weight-per-construction-area approximation; national estimates using alternative procedures such as those used for other segments of the solid waste stream have not been reported for C&D debris. This paper presents an evaluation of a materials flow analysis (MFA) approach for estimating C&D debris generation and composition for a large region (the US). The consumption of construction materials in the US and typical waste factors used for construction materials purchasing were used to estimate the mass of solid waste generated as a result of construction activities. Debris from demolition activities was predicted from various historical construction materials consumption data and estimates of average service lives of the materials. The MFA approach estimated that approximately 610-78 × 10(6)Mg of C&D debris was generated in 2002. This predicted mass exceeds previous estimates using other C&D debris predictive methodologies and reflects the large waste stream that exists.
A computationally practical approach for modeling complex mean flows in mildly heterogeneous media
NASA Astrophysics Data System (ADS)
Li, Shu-Guang; Liao, H. S.; Ni, Chuen-Fa
2004-12-01
We present in this paper a critical review of recent research on nonuniform mean flows in heterogeneous porous media, examine why existing stochastic methods are computationally so difficult to implement, and introduce a new and efficient alternative. Specifically, we reformulate the nonstationary spectral method of Li and McLaughlin (1991, 1995) and present a new way for its numerical implementation, combining the best advantages of efficient analytical solutions and flexible numerical techniques. The result is a substantially improved stochastic technique that allows modeling efficiently the nonlinear scale effects for moderately heterogeneous media in the presence of general nonstationarity. In particular, the reformulated approach allows computing the nonlocal and nonstationary mean "closure" flux using a coarse grid without having to resolve numerically the small-scale heterogeneous dynamics. The methodological innovation significantly increases the size and expands the range of groundwater problems that can be analyzed with stochastic methods. The effectiveness of the new spectral approach is illustrated with two concrete examples and a systematic comparison with existing stochastic methods.
Mansilla Alvarez, Luis; Blanco, Pablo; Bulant, Carlos; Dari, Enzo; Veneziani, Alessandro; Feijóo, Raúl
2017-04-01
In this work, we present a novel approach tailored to approximate the Navier-Stokes equations to simulate fluid flow in three-dimensional tubular domains of arbitrary cross-sectional shape. The proposed methodology is aimed at filling the gap between (cheap) one-dimensional and (expensive) three-dimensional models, featuring descriptive capabilities comparable with the full and accurate 3D description of the problem at a low computational cost. In addition, this methodology can easily be tuned or even adapted to address local features demanding more accuracy. The numerical strategy employs finite (pipe-type) elements that take advantage of the pipe structure of the spatial domain under analysis. While low order approximation is used for the longitudinal description of the physical fields, transverse approximation is enriched using high order polynomials. Although our application of interest is computational hemodynamics and its relevance to pathological dynamics like atherosclerosis, the approach is quite general and can be applied in any internal fluid dynamics problem in pipe-like domains. Numerical examples covering academic cases as well as patient-specific coronary arterial geometries demonstrate the potentialities of the developed methodology and its performance when compared against traditional finite element methods. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.
Smith, J B; Calder, F R
2008-01-01
High flow fistulae present a common challenge to vascular access (VA) surgeons and many strategies have been described, each with their benefits and limitations. There are no NK-DOQI guidelines for the management of high flow fistulae or indeed the management of those refractory to more conventional approaches. We discuss a novel technique to inflow reduction in a previously distalized brachiocephalic fistula and recommend the technique of proximal radial artery ligation.
Wang, J.S.Y.; Narasimhan, T.N.
1993-06-01
This report discusses conceptual models and mathematical equations, analyzes distributions and correlations among hydrological parameters of soils and tuff, introduces new path integration approaches, and outlines scaling procedures to model potential-driven fluid flow in heterogeneous media. To properly model the transition from fracture-dominated flow under saturated conditions to matrix-dominated flow under partially saturated conditions, characteristic curves and permeability functions for fractures and matrix need to be improved and validated. Couplings from two-phase flow, heat transfer, solute transport, and rock deformation to liquid flow are also important. For stochastic modeling of alternating units of welded and nonwelded tuff or formations bounded by fault zones, correlations and constraints on average values of saturated permeability and air entry scaling factor between different units need to be imposed to avoid unlikely combinations of parameters and predictions. Large-scale simulations require efficient and verifiable numerical algorithms. New path integration approaches based on postulates of minimum work and mass conservation to solve flow geometry and potential distribution simultaneously are introduced. This verifiable integral approach, together with fractal scaling procedures to generate statistical realizations with parameter distribution, correlation, and scaling taken into account, can be used to quantify uncertainties and generate the cumulative distribution function for groundwater travel times.
Hughes, Francine M R; Rood, Stewart B
2003-07-01
Floodplain forests are flood-dependent ecosystems. They rely on well-timed, periodic floods for the provision of regeneration sites and on tapered flood recession curves for the successful establishment of seedlings. These overbank flood events are described as "regeneration flows." Once floodplain forest trees are established, in order to grow they also require adequate, although variable, river stage levels or "maintenance flows" throughout the year. Regeneration flows are often synonymous with flood flows and only occur periodically. There is a disparity between this need for varied interannual flows over the decadal time frame and the usual annual cycle of flow management currently used by most river management agencies. Maintenance flows are often closer to established minimum flows and much easier to provide by current operational practices.A number of environmental flow methodologies, developed in North America, Australia, and South Africa are described in this review. They include the needs of the floodplain environment in the management and allocation of river flows. In North America, these methodologies have been put into practice in a number of river basins specifically to restore floodplain forest ecosystems. In Australia and South Africa, a series of related "holistic approaches" have been developed that include the needs of floodplain ecosystems as well as in-channel ecosystems. In most European countries, restoration of floodplain forests takes place at a few localized restoration sites, more often as part of a flood-defense scheme and usually not coordinated with flow allocation decisions throughout the river basin. The potential to apply existing environmental flow methodologies to the management of European floodplain forests is discussed.
Fratto, Brian E; Katz, Evgeny
2015-05-18
Reversible logic gates, such as the double Feynman gate, Toffoli gate and Peres gate, with 3-input/3-output channels are realized using reactions biocatalyzed with enzymes and performed in flow systems. The flow devices are constructed using a modular approach, where each flow cell is modified with one enzyme that biocatalyzes one chemical reaction. The multi-step processes mimicking the reversible logic gates are organized by combining the biocatalytic cells in different networks. This work emphasizes logical but not physical reversibility of the constructed systems. Their advantages and disadvantages are discussed and potential use in biosensing systems, rather than in computing devices, is suggested.
Ensuring the consistancy of Flow Direction Curve reconstructions: the 'quantile solidarity' approach
NASA Astrophysics Data System (ADS)
Poncelet, Carine; Andreassian, Vazken; Oudin, Ludovic
2015-04-01
Flow Duration Curves (FDCs) are a hydrologic tool describing the distribution of streamflows at a catchment outlet. FDCs are usually used for calibration of hydrological models, managing water quality and classifying catchments, among others. For gauged catchments, empirical FDCs can be computed from streamflow records. For ungauged catchments, on the other hand, FDCs cannot be obtained from streamflow records and must therefore be obtained in another manner, for example through reconstructions. Regression-based reconstructions are methods relying on the evaluation of quantiles separately from catchments' attributes (climatic or physical features).The advantage of this category of methods is that it is informative about the processes and it is non-parametric. However, the large number of parameters required can cause unwanted artifacts, typically reconstructions that do not always produce increasing quantiles. In this paper we propose a new approach named Quantile Solidarity (QS), which is applied under strict proxy-basin test conditions (Klemes, 1986) to a set of 600 French catchments. Half of the catchments are considered as gauged and used to calibrate the regression and compute residuals of the regression. The QS approach consists in a three-step regionalization scheme, which first links quantile values to physical descriptors, then reduces the number of regression parameters and finally exploits the spatial correlation of the residuals. The innovation is the utilisation of the parameters continuity across the quantiles to dramatically reduce the number of parameters. The second half of catchment is used as an independent validation set over which we show that the QS approach ensures strictly growing FDC reconstructions in ungauged conditions. Reference: V. KLEMEŠ (1986) Operational testing of hydrological simulation models, Hydrological Sciences Journal, 31:1, 13-24
Su, Kuan-Hao; Yen, Tzu-Chen; Fang, Yu-Hua Dean
2013-10-01
The aim of this study is to develop and evaluate a novel direct reconstruction method to improve the signal-to-noise ratio (SNR) of parametric images in dynamic positron-emission tomography (PET), especially for applications in myocardial perfusion studies. Simulation studies were used to test the performance in SNR and computational efficiency for different methods. The NCAT phantom was used to generate simulated dynamic data. Noise realization was performed in the sinogram domain and repeated for 30 times with four different noise levels by varying the injection dose (ID) from standard ID to 1/8 of it. The parametric images were calculated by (1) three direct methods that compute the kinetic parameters from the sinogram and (2) an indirect method, which computes the kinetic parameter with pixel-by-pixel curve fitting in image space using weighted least-squares. The first direct reconstruction maximizes the likelihood function using trust-region-reflective (TRR) algorithm. The second approach uses tabulated parameter sets to generate precomputed time-activity curves for maximizing the likelihood functions. The third approach, as a newly proposed method, assumes separable complete data to derive the M-step for maximizing the likelihood. The proposed method with the separable complete data performs similarly to the other two direct reconstruction methods in terms of the SNR, providing a 5%-10% improvement as compared to the indirect parametric reconstruction under the standard ID. The improvement of SNR becomes more obvious as the noise level increases, reaching more than 30% improvement under 1/8 ID. Advantage of the proposed method lies in the computation efficiency by shortening the time requirement to 25% of the indirect approach and 3%-6% of other direct reconstruction methods. With results provided from this simulation study, direct reconstruction of myocardial blood flow shows a high potential for improving the parametric image quality for clinical use.
Shahgaldi, Kambiz; Söderqvist, Emil; Gudmundsson, Petri; Winter, Reidar; Nowak, Jacek; Brodin, Lars-Åke
2008-01-01
Background This study explores the feasibility of non-invasive evaluation of left ventricular (LV) flow-volume dynamics using 3-dimensional (3D) echocardiography, and the capacity of such an approach to identify altered LV hemodynamic states caused by valvular abnormalities. Methods Thirty-one patients with moderate-severe aortic (AS) and mitral (MS) stenoses (21 and 10 patients, respectively) and 10 healthy volunteers underwent 3D echocardiography with full volume acquisition using Philips Sonos 7500 equipment. The digital 3D data were post- processed using TomTec software. LV flow-volume loops were subsequently constructed for each subject by plotting instantaneous LV volume data sampled throughout the cardiac cycle vs. their first derivative representing LV flow. After correction for body surface area, an average flow-volume loop was calculated for each subject group. Results Flow-volume loops were obtainable in all subjects, except 3 patients with AS. The flow-volume diagrams displayed clear differences in the form and position of the loops between normal individuals and the respective patient groups. In patients with AS, an "obstructive" pattern was observed, with lower flow values during early systole and larger end-systolic volume. On the other hand, patients with MS displayed a "restrictive" flow-volume pattern, with reduced diastolic filling and smaller end-diastolic volume. Conclusion Non-invasive evaluation of LV flow-volume dynamics using 3D-echocardiographic data is technically possible and the approach has a capacity to identify certain specific types of alteration of LV flow-volume pattern caused by valvular abnormalities, thus reflecting underlying hemodynamic states specific for these abnormalities. PMID:18394157
Alonso, Carlos; Román, Alfonso; Bejarano, Maria Dolores; Garcia de Jalon, Diego; Carolli, Mauro
2017-01-01
Most flow regime characterizations focus on long time scale flow patterns, which are not precise enough to capture key components of short-term flow fluctuations. Recent proposed methods describing sub-daily flow fluctuations are focused on limited components of the flow regime being unable to fully represent it, or on the identification of peaking events based on subjectively defined thresholds, being unsuitable for evaluations of short-term flow regime alterations through comparisons between regulated and free-flowing rivers. This study aims to launch an innovative approach based on the visual display of quantitative information to address the challenge of the short-term hydrologic characterization and evaluation of alteration resulting from hydropeaking. We propose a graphical method to represent a discrete set of ecologically relevant indices that characterize and evaluate the alteration of sub-daily flow regimes. The frequency of occurrence of classified values of a descriptive hydrological variable is represented in a map-like graph where longitude, latitude and altitude represent the Julian day, the value of the variable and the frequency of occurrence, respectively. Subsequently, we tested the method on several rivers, both free-flowing and subjected to hydropower production. The advantages of our approach compared to other analytical methods are: (i) it displays a great amount of information without oversimplification; (ii) it takes into account changes in the intensity, timing and frequency of the sub-daily flows, without needing a priori defined thresholds to identify hydropeaking events; and (iii) it supports the Water Framework Directive goal. Specifically, results from applications of our graphical method agree with Sauterleute and Charmasson (2014) analytical method.
Modelling transverse turbulent mixing in a shallow flow by using an eddy viscosity approach
NASA Astrophysics Data System (ADS)
Gualtieri, C.
2009-04-01
The mixing of contaminants in streams and rivers is a significant problem in environmental fluid mechanics and rivers engineering since to understand the impact and the fate of pollutants in these water bodies is a primary goal of water quality management. Since most rivers have a high aspect ratio, that is the width to depth ratio, discharged pollutants become vertically mixed within a short distance from the source and vertical mixing is only important in the so-called near-field. As a rule of thumb, neutrally buoyant solute becomes fully mixed vertically within 50-75 depths from the source. Notably, vertical mixing analysis relies on well-known theoretical basis, that is Prandtl mixing length model, which assumes the hypothesis of plane turbulent shear flow and provides theoretical predictions of the vertical turbulent diffusivity which closely match experimental results. In the mid-field, the vertical concentration gradients are negligible and both subsequent transverse and longitudinal changes of the depth-averaged concentrations of the pollutants should be addressed. In the literature, for the application of one-dimensional water quality models the majority of research efforts were devoted to estimate the rate of longitudinal mixing of a contaminant, that is the development of a plume resulting from a temporally varying pollutant source once it has become cross-sectionally well-mixed, in the far-field. Although transverse mixing is a significant process in river engineering when dealing with the discharge of pollutants from point sources or the mixing of tributary inflows, no theoretical basis exists for the prediction of its rate, which is indeed based upon the results of experimental works carried on in laboratory channels or in streams and rivers. Turbulence models based on the eddy viscosity approach, such as the k-É model, k-? and their variation are the most widely used turbulence models and this is largely due to their ease in implementation
NASA Astrophysics Data System (ADS)
Valdarnini, R.
2016-11-01
In this paper, we present results from a series of hydrodynamical tests aimed at validating the performance of a smoothed particle hydrodynamics (SPH) formulation in which gradients are derived from an integral approach. We specifically investigate the code behavior with subsonic flows, where it is well known that zeroth-order inconsistencies present in standard SPH make it particularly problematic to correctly model the fluid dynamics. In particular, we consider the Gresho-Chan vortex problem, the growth of Kelvin-Helmholtz instabilities, the statistics of driven subsonic turbulence and the cold Keplerian disk problem. We compare simulation results for the different tests with those obtained, for the same initial conditions, using standard SPH. We also compare the results with the corresponding ones obtained previously with other numerical methods, such as codes based on a moving-mesh scheme or Godunov-type Lagrangian meshless methods. We quantify code performances by introducing error norms and spectral properties of the particle distribution, in a way similar to what was done in other works. We find that the new SPH formulation exhibits strongly reduced gradient errors and outperforms standard SPH in all of the tests considered. In fact, in terms of accuracy, we find good agreement between the simulation results of the new scheme and those produced using other recently proposed numerical schemes. These findings suggest that the proposed method can be successfully applied for many astrophysical problems in which the presence of subsonic flows previously limited the use of SPH, with the new scheme now being competitive in these regimes with other numerical methods.
NASA Astrophysics Data System (ADS)
Piotrowski, Adam P.; Napiorkowski, Jarosław J.
2011-09-01
SummaryAlthough neural networks have been widely applied to various hydrological problems, including river flow forecasting, for at least 15 years, they have usually been trained by means of gradient-based algorithms. Recently nature inspired Evolutionary Computation algorithms have rapidly developed as optimization methods able to cope not only with non-differentiable functions but also with a great number of local minima. Some of proposed Evolutionary Computation algorithms have been tested for neural networks training, but publications which compare their performance with gradient-based training methods are rare and present contradictory conclusions. The main goal of the present study is to verify the applicability of a number of recently developed Evolutionary Computation optimization methods, mostly from the Differential Evolution family, to multi-layer perceptron neural networks training for daily rainfall-runoff forecasting. In the present paper eight Evolutionary Computation methods, namely the first version of Differential Evolution (DE), Distributed DE with Explorative-Exploitative Population Families, Self-Adaptive DE, DE with Global and Local Neighbors, Grouping DE, JADE, Comprehensive Learning Particle Swarm Optimization and Efficient Population Utilization Strategy Particle Swarm Optimization are tested against the Levenberg-Marquardt algorithm - probably the most efficient in terms of speed and success rate among gradient-based methods. The Annapolis River catchment was selected as the area of this study due to its specific climatic conditions, characterized by significant seasonal changes in runoff, rapid floods, dry summers, severe winters with snowfall, snow melting, frequent freeze and thaw, and presence of river ice - conditions which make flow forecasting more troublesome. The overall performance of the Levenberg-Marquardt algorithm and the DE with Global and Local Neighbors method for neural networks training turns out to be superior to other
NASA Astrophysics Data System (ADS)
Lehikoinen, A.; Finsterle, S.; Voutilainen, A.; Kowalsky, M.; Kaipio, J.
2006-12-01
We present a new methodology for imaging the evolution of electrically conductive fluids in porous media. The state estimation problem is formulated in terms of an evolution-observation model, and the estimates are obtained via Bayesian filtering. The approach is based on an extended Kalman filter algorithm and includes an approximation error method to model uncertainties in the evolution and observation models. The example we consider involves the imaging of time-varying distributions of water saturation in porous media using time-lapse electrical resistance tomography (ERT). The evolution model we employ is a simplified model for simulating flow through partially saturated porous media. The complete electrode model (with Archie's law relating saturations to electrical conductivity) is used as the observation model. We propose to account for approximation errors in the evolution and observation models by constructing a statistical model of the differences between the "accurate" and "approximate" representations of fluid flow, and by including this information in the calculation of the posterior probability density of the estimated system state. The proposed method provides improved estimates of water saturation distribution relative to traditional reconstruction schemes that rely on conventional stabilization methods (e.g., using a smoothness prior) and relative to the extended Kalman filter without the approximation error method incorporated. Finally, the approximation error method allows for the use of a simplified and computationally efficient evolution model in the state estimation scheme. This work was supported, in part, by the Finnish Funding Agency for Technology and Innovation (TEKES), projects 40285/05 and 40347/05, and by the U.S. Dept. of Energy under Contract No. DE-AC02- 05CH11231.
A parallel multi-block/multi-physics approach for multi-phase flow in porous media
NASA Astrophysics Data System (ADS)
Lu, Qin
The main purpose of this dissertation is to investigate accurate and efficient numerical techniques for simulation of multi-phase/multi-component flow and transport phenomena in porous media which are of major importance in the petroleum and environmental industries. We propose to emphasize a novel numerical methodology, which is called the multi-block algorithm. This algorithm is based on the decomposition of the simulation domain into multiple non-overlapping subdomains (blocks) according to the geological, geometric and physical/chemical properties. One then applies the most suitable grid, numerical scheme and physical model in each subdomain, so that the computational cost is reduced and accuracy is preserved. Across the interface of neighboring subdomains, the consistent primary variables and the continuity of the component mass fluxes are imposed in a weak sense. In this dissertation we first discuss the mathematical and numerical formulations of physical models, such as the implicit black-oil model, the implicit and IMPES two-phase hydrology models. We then formulate the multi-block black-oil model coupling different grids, which can be non-matching on the interface. In addition, we define the multi-model couplings; in particular, the coupling of the implicit and IMPES schemes for two-phase immiscible flow, and the coupling of the implicit three-phase black-oil model and the implicit two-phase hydrology model. Computational examples are presented to demonstrate the scalability of the multi-block/multi-model simulators over the traditional single-block/single-model simulators. Excellent agreements of the results between these two approaches are shown. Parallel computation issues, especially the MPI (Message Passing Interface) multi-communicator implementation and model-based load balancing strategies for the parallelism of the multi-model problem are also considered. Summary of these results is presented in the last chapter.
NASA Astrophysics Data System (ADS)
Mierzwiczak, M.; Grabski, J. K.; Kołodziej, J. A.
2016-10-01
In the paper three different approaches for the Trefftz method are compared in analysis of the fluid flow between regular bundles of cylindrical fibres. The approximate solution is a linear combination of such trial functions which fulfil exactly the governing equations. The trial functions can be defined in the Cartesian coordinate system (the first approach), in the cylindrical coordinate system (and can fulfil also some boundary conditions - the second approach) or be defined as a fundamental solutions (the third approach - the method of fundamental solutions).The average velocity and the product of the friction factor and the Reynolds number ƒ ṡ Re are compared for selected parameters of a considered region.
Glahn, A.; Kurreck, M.; Willmann, M.; Wittig, S.
1996-10-01
The present paper deals with oil droplet flow phenomena in aero engine bearing chambers. An experimental investigation of droplet sizes and velocities utilizing a Phase Doppler Particle Analyzer (PDPA) has been performed for the first time in bearing chamber atmospheres under real engine conditions. Influences of high rotational speeds are discussed for individual droplet size classes. Although this is an important contribution to a better understanding of the droplet flow impact on secondary air/oil system performance, an analysis of the droplet flow behavior requires an incorporation of numerical methods because detailed measurements as performed here suffer from both strong spatial limitations with respect to the optical accessibility in real engine applications and constraints due to the extremely time-consuming nature of an experimental flow field analysis. Therefore, further analysis is based on numerical methods. Droplets characterized within the experiments are exposed to the flow field of the gaseous phase predicted by use of the well-known CFD code EPOS. The droplet trajectories and velocities are calculated within a Lagrangian frame of reference by forward numerical integration of the particle momentum equation. This paper has been initiated rather to show a successful method of bearing chamber droplet flow analysis by a combination of droplet sizing techniques and numerical approaches than to present field values as a function of all operating parameters. However, a first insight into the complex droplet flow phenomena is given and specific problems in bearing chamber heat transfer are related to the droplet flow.
NASA Astrophysics Data System (ADS)
Mirus, Benjamin B.; Nimmo, John R.
2013-03-01
The impact of preferential flow on recharge and contaminant transport poses a considerable challenge to water-resources management. Typical hydrologic models require extensive site characterization, but can underestimate fluxes when preferential flow is significant. A recently developed source-responsive model incorporates film-flow theory with conservation of mass to estimate unsaturated-zone preferential fluxes with readily available data. The term source-responsive describes the sensitivity of preferential flow in response to water availability at the source of input. We present the first rigorous tests of a parsimonious formulation for simulating water table fluctuations using two case studies, both in arid regions with thick unsaturated zones of fractured volcanic rock. Diffuse flow theory cannot adequately capture the observed water table responses at both sites; the source-responsive model is a viable alternative. We treat the active area fraction of preferential flow paths as a scaled function of water inputs at the land surface then calibrate the macropore density to fit observed water table rises. Unlike previous applications, we allow the characteristic film-flow velocity to vary, reflecting the lag time between source and deep water table responses. Analysis of model performance and parameter sensitivity for the two case studies underscores the importance of identifying thresholds for initiation of film flow in unsaturated rocks, and suggests that this parsimonious approach is potentially of great practical value.
Mirus, Benjamin B.; Nimmo, J.R.
2013-01-01
The impact of preferential flow on recharge and contaminant transport poses a considerable challenge to water-resources management. Typical hydrologic models require extensive site characterization, but can underestimate fluxes when preferential flow is significant. A recently developed source-responsive model incorporates film-flow theory with conservation of mass to estimate unsaturated-zone preferential fluxes with readily available data. The term source-responsive describes the sensitivity of preferential flow in response to water availability at the source of input. We present the first rigorous tests of a parsimonious formulation for simulating water table fluctuations using two case studies, both in arid regions with thick unsaturated zones of fractured volcanic rock. Diffuse flow theory cannot adequately capture the observed water table responses at both sites; the source-responsive model is a viable alternative. We treat the active area fraction of preferential flow paths as a scaled function of water inputs at the land surface then calibrate the macropore density to fit observed water table rises. Unlike previous applications, we allow the characteristic film-flow velocity to vary, reflecting the lag time between source and deep water table responses. Analysis of model performance and parameter sensitivity for the two case studies underscores the importance of identifying thresholds for initiation of film flow in unsaturated rocks, and suggests that this parsimonious approach is potentially of great practical value.
Sagaidachnyi, A A; Fomin, A V; Usanov, D A; Skripal, A V
2017-02-01
The determination of the relationship between skin blood flow and skin temperature dynamics is the main problem in thermography-based blood flow imaging. Oscillations in skin blood flow are the source of thermal waves propagating from micro-vessels toward the skin's surface, as assumed in this study. This hypothesis allows us to use equations for the attenuation and dispersion of thermal waves for converting the temperature signal into the blood flow signal, and vice versa. We developed a spectral filtering approach (SFA), which is a new technique for thermography-based blood flow imaging. In contrast to other processing techniques, the SFA implies calculations in the spectral domain rather than in the time domain. Therefore, it eliminates the need to solve differential equations. The developed technique was verified within 0.005-0.1 Hz, including the endothelial, neurogenic and myogenic frequency bands of blood flow oscillations. The algorithm for an inverse conversion of the blood flow signal into the skin temperature signal is addressed. The examples of blood flow imaging of hands during cuff occlusion and feet during heating of the back are illustrated. The processing of infrared (IR) thermograms using the SFA allowed us to restore the blood flow signals and achieve correlations of about 0.8 with a waveform of a photoplethysmographic signal. The prospective applications of the thermography-based blood flow imaging technique include non-contact monitoring of the blood supply during engraftment of skin flaps and burns healing, as well the use of contact temperature sensors to monitor low-frequency oscillations of peripheral blood flow.
NASA Astrophysics Data System (ADS)
Marjoribanks, T. I.; Hardy, R. J.; Lane, S. N.; Parsons, D. R.
2012-12-01
The flow and plant dynamics of vegetated channel flows are governed by a variety of processes and feedback mechanisms that interact, across a range of scales, to form a complex inter-connected system. It is well documented that vegetation exerts a significant drag force on the flow, creating a drag discontinuity between the canopy layer and the flow above. This has been shown to control the mean flow and turbulent structure through the development of a canopy shear layer, which leads to the generation of coherent roller vortices at the canopy top. In turn, the canopy reacts to the flow forcing through reconfiguration to minimize drag, and responds to the passage of vortices through exhibiting coherent monami. It has been hypothesized that the vegetation consequently acts to modulate the turbulence structure through the vibrational response of the natural frequency of the vegetation. Hence the interaction of processes is complex and nonlinear. Here we report on a series of high resolution numerical experiments designed to investigate the exact nature and role of these feedback mechanisms within the flow-vegetation system. Two biomechanical models are developed and applied within a computational fluid dynamics framework to investigate the nature of the time-dependent flow dynamics. The first model, for semi-flexible vegetation uses the Euler Beam equation to drive plant motion, whilst the second model uses an n-pendula approach to represent cases of highly flexible vegetation. Both models were validated through a series of laboratory experiments using particle image velocimetry that employed both real and prototype vegetation. The high-resolution numerical models enable detailed analysis of both the plant motion and corresponding flow field. The results clearly show the presence of a strong drag discontinuity, coherent canopy motion and large scale turbulent structures formed at the canopy top. Time series and spectral analysis reveals a clear, time
Intercomparison of Multiscale Modeling Approaches in Simulating Subsurface Flow and Transport
NASA Astrophysics Data System (ADS)
Yang, X.; Mehmani, Y.; Barajas-Solano, D. A.; Song, H. S.; Balhoff, M.; Tartakovsky, A. M.; Scheibe, T. D.
2016-12-01
Hybrid multiscale simulations that couple models across scales are critical to advance predictions of the larger system behavior using understanding of fundamental processes. In the current study, three hybrid multiscale methods are intercompared: multiscale loose-coupling method, multiscale finite volume (MsFV) method and multiscale mortar method. The loose-coupling method enables a parallel workflow structure based on the Swift scripting environment that manages the complex process of executing coupled micro- and macro-scale models without being intrusive to the at-scale simulators. The MsFV method applies microscale and macroscale models over overlapping subdomains of the modeling domain and enforces continuity of concentration and transport fluxes between models via restriction and prolongation operators. The mortar method is a non-overlapping domain decomposition approach capable of coupling all permutations of pore- and continuum-scale models with each other. In doing so, Lagrange multipliers are used at interfaces shared between the subdomains so as to establish continuity of species/fluid mass flux. Subdomain computations can be performed either concurrently or non-concurrently depending on the algorithm used. All the above methods have been proven to be accurate and efficient in studying flow and transport in porous media. However, there has not been any field-scale applications and benchmarking among various hybrid multiscale approaches. To address this challenge, we apply all three hybrid multiscale methods to simulate water flow and transport in a conceptualized 2D modeling domain of the hyporheic zone, where strong interactions between groundwater and surface water exist across multiple scales. In all three multiscale methods, fine-scale simulations are applied to a thin layer of riverbed alluvial sediments while the macroscopic simulations are used for the larger subsurface aquifer domain. Different numerical coupling methods are then applied between
A Many-Task Parallel Approach for Multiscale Simulations of Subsurface Flow and Reactive Transport
Scheibe, Timothy D.; Yang, Xiaofan; Schuchardt, Karen L.; Agarwal, Khushbu; Chase, Jared M.; Palmer, Bruce J.; Tartakovsky, Alexandre M.
2014-12-16
Continuum-scale models have long been used to study subsurface flow, transport, and reactions but lack the ability to resolve processes that are governed by pore-scale mixing. Recently, pore-scale models, which explicitly resolve individual pores and soil grains, have been developed to more accurately model pore-scale phenomena, particularly reaction processes that are controlled by local mixing. However, pore-scale models are prohibitively expensive for modeling application-scale domains. This motivates the use of a hybrid multiscale approach in which continuum- and pore-scale codes are coupled either hierarchically or concurrently within an overall simulation domain (time and space). This approach is naturally suited to an adaptive, loosely-coupled many-task methodology with three potential levels of concurrency. Each individual code (pore- and continuum-scale) can be implemented in parallel; multiple semi-independent instances of the pore-scale code are required at each time step providing a second level of concurrency; and Monte Carlo simulations of the overall system to represent uncertainty in material property distributions provide a third level of concurrency. We have developed a hybrid multiscale model of a mixing-controlled reaction in a porous medium wherein the reaction occurs only over a limited portion of the domain. Loose, minimally-invasive coupling of pre-existing parallel continuum- and pore-scale codes has been accomplished by an adaptive script-based workflow implemented in the Swift workflow system. We describe here the methods used to create the model system, adaptively control multiple coupled instances of pore- and continuum-scale simulations, and maximize the scalability of the overall system. We present results of numerical experiments conducted on NERSC supercomputing systems; our results demonstrate that loose many-task coupling provides a scalable solution for multiscale subsurface simulations with minimal overhead.
Habib, Komal; Schibye, Peter Klausen; Vestbø, Andreas Peter; Dall, Ole; Wenzel, Henrik
2014-10-21
Neodymium-iron-boron (NdFeB) magnets have become highly desirable for modern hi-tech applications. These magnets, in general, contain two key rare earth elements (REEs), i.e., neodymium (Nd) and dysprosium (Dy), which are responsible for the very high strength of these magnets, allowing for considerable size and weight reduction in modern applications. This study aims to explore the current and future potential of a secondary supply of neodymium and dysprosium from recycling of NdFeB magnets. For this purpose, material flow analysis (MFA) has been carried out to perform the detailed mapping of stocks and flows of NdFeB magnets in Denmark. A novel element of this study is the value added to the traditionally practiced MFAs at national and/or global levels by complementing them with a comprehensive sampling and elemental analysis of NdFeB magnets, taken out from a sample of 157 different products representing 18 various product types. The results show that the current amount of neodymium and dysprosium in NdFeB magnets present in the Danish waste stream is only 3 and 0.2 Mg, respectively. However, this number is estimated to increase to 175 Mg of neodymium and 11.4 Mg of dysprosium by 2035. Nevertheless, efficient recovery of these elements from a very diverse electronic waste stream remains a logistic and economic challenge.
A Basic Approach to Lymph Node and Flow Cytometry Fine-Needle Cytology.
Barroca, Helena; Marques, Cristina
2016-01-01
According to the World Health Organization (WHO), the new classification of lymphomas is mainly based on morphological, immunophenotypical, and molecular criteria. Consequently, this new approach has led from the substantial role that architecture played in the past to a secondary panel highlighting the role of fine-needle biopsy (FNB). Applied together with other ancillary techniques, such as flow cytometry (FC), FNB is a potential tool for the diagnosis of lymphomas, and enlarged lymph nodes represent an excellent target for the implementation of this technique. Despite the difficulties inherent in this technology, which might pose problems in differential diagnosis, in the majority of cases this joint work allows an accurate diagnosis of malignancy and even correct subcharacterization in routine lymphomas. Additionally, in selected cases, other molecular techniques like FISH and PCR can also be performed on FNB specimens, helping in the characterization and diagnosis of lymphomas. In this review, we discuss the basic aspects of the combination of FNB cytology and FC in the diagnosis and subclassification of lymphomas. The preanalytical phase is extensively discussed. The advantages, disadvantages, and technical limitations of this joint work are addressed in general and in terms of the accurate subclassification of lymphomas. © 2016 S. Karger AG, Basel.
NASA Astrophysics Data System (ADS)
Ianoul, Anatoli I.; Fleury, Fabrice; Duval, Olivier; Jardillier, Jean-Claude; Alix, Alain J.; Nabiev, Igor R.
1999-04-01
Surface-Enhanced Raman Scattering (SERS) spectroscopy and Flow Linear Dichroism (FLD) technique have been employed to study the anticancer agent fagaronine and its derivative ethoxidine - double inhibitors of DNA topoisomerases I and II. Cooperative use of two methods permitted (i) to determine the molecular determinants of the drug-DNA interactions; (ii) to monitor in real time the process of topo I inhibition by these anticancer agents. FLD technique allowed us to identify the mode of drug interactions with the DNA as a 'major groove intercalation' and to determine orientation of the drugs chromophores within the complexes. Using SERS spectroscopy we have determined the drugs molecular determinants interacting with the DNA. FLD was also used for real time monitoring of the process of sc DNA relaxation by topo I and of inhibition of relaxation with the pharmaceuticals. Ethoxidine was found to exhibit the same activity of inhibition of sc DNA relaxation as fagaronine at the 10-fold less concentration. The proposed SERS-FLD combined approach demonstrates the new perspectives for screening new pharmaceuticals due to its relative simplicity and low expense, high sensitivity and selectivity, and, finally, possibility of real-time monitoring of the structure-function correlation within the series of drug derivatives.
An approximate viscous shock layer approach to calculating hypersonic flows about blunt-nosed bodies
NASA Technical Reports Server (NTRS)
Cheatwood, F. MCN.; Dejarnette, F. R.
1991-01-01
An approximate axisymmetric method has been developed which can reliably calculate fully viscous hypersonic flows over blunt-nosed bodies. By substituting Maslen's second order pressure expression for the normal momentum equation, a simplified form of the viscous shock layer (VSL) equations is obtained. This approach can solve both the subsonic and supersonic regions of the shock layer without a starting solution for the shock shape. Since the method is fully viscous, the problems associated with coupling a boundary-layer solution with an inviscid-layer solution are avoided. This procedure is significantly faster than the parabolized Navier-Stokes (PNS) or VSL solvers and would be useful in a preliminary design environment. Problems associated with a previously developed approximate VSL technique are addressed. Surface heat transfer and pressure predictions are comparable to both VSL results and experimental data. The present technique generates its own shock shape as part of its solution, and therefore could be used to provide more accurate initial shock shapes for higher-order procedures which require starting solutions.
Vibration transmission through periodic structures using a mobility power flow approach
NASA Technical Reports Server (NTRS)
Cuschieri, J. M.
1990-01-01
The transmission of vibrational power (time averaged) through multiple coupled (periodic) structures is examined. The analysis is performed in the frequency domain and the coupling between the sub-elements of the periodic structure is expressed in terms of structural mobility functions for the junction points and between the junction points of the sub-elements. Equal length spans between stiffeners or supports of the periodic structure are considered. Through the use of the mobility power flow approach, the influence of sub-element and junction parameters, including damping at the joints, can be investigated. The results from the analysis can be in the form of either structural intensity or alternatively structural power content for each of the sub-elements. The examples discussed are for a thin, perfectly periodic beam with a finite number of spans with different types of stiffeners and/or supports between the spans. The excitation of the structure is by a point load located midway along the first span.
Vibration transmission through periodic structures using a mobility power flow approach
NASA Technical Reports Server (NTRS)
Cuschieri, J. M.
1990-01-01
The transmission of vibrational power (time averaged) through multiple coupled (periodic) structures is examined. The analysis is performed in the frequency domain and the coupling between the sub-elements of the periodic structure is expressed in terms of structural mobility functions for the junction points and between the junction points of the sub-elements. Equal length spans between stiffeners or supports of the periodic structure are considered. Through the use of the mobility power flow approach, the influence of sub-element and junction parameters, including damping at the joints, can be investigated. The results from the analysis can be in the form of either structural intensity or alternatively structural power content for each of the sub-elements. The examples discussed are for a thin, perfectly periodic beam with a finite number of spans with different types of stiffeners and/or supports between the spans. The excitation of the structure is by a point load located midway along the first span.
Bayesian and variational Bayesian approaches for flows in heterogeneous random media
NASA Astrophysics Data System (ADS)
Yang, Keren; Guha, Nilabja; Efendiev, Yalchin; Mallick, Bani K.
2017-09-01
In this paper, we study porous media flows in heterogeneous stochastic media. We propose an efficient forward simulation technique that is tailored for variational Bayesian inversion. As a starting point, the proposed forward simulation technique decomposes the solution into the sum of separable functions (with respect to randomness and the space), where each term is calculated based on a variational approach. This is similar to Proper Generalized Decomposition (PGD). Next, we apply a multiscale technique to solve for each term (as in [1]) and, further, decompose the random function into 1D fields. As a result, our proposed method provides an approximation hierarchy for the solution as we increase the number of terms in the expansion and, also, increase the spatial resolution of each term. We use the hierarchical solution distributions in a variational Bayesian approximation to perform uncertainty quantification in the inverse problem. We conduct a detailed numerical study to explore the performance of the proposed uncertainty quantification technique and show the theoretical posterior concentration.
NASA Astrophysics Data System (ADS)
Lipponen, A.; Seppänen, A.; Kaipio, J. P.
2011-10-01
In this paper, we consider nonstationary estimation in imaging of three-dimensional fluid flow. More specifically, we experimentally evaluate the feasibility of a recently invented approximation error method to recovering from modelling errors in imaging of nonstationary targets. In nonstationary estimation, both the observations and the time evolution of the target distribution are modelled, and the image reconstruction problem is written in the form of a state estimation problem. The state estimates rely on these models and the observations carried out during the evolution of the target. If the associated modelling errors are not accounted for, state estimation can lead to heavily biased reconstructions. In the approximation error approach, the model inaccuracies and uncertainties are modelled statistically. In this experimental study, we consider a case of rapidly moving fluid in a pipeline, and model the target with the convection-diffusion equation. Electrical impedance tomography (EIT) is used as the imaging modality. In the nonstationary approximation error scheme, we model the errors due to truncation of the computational domain, discretization, unknown contact impedances of electrodes used in EIT measurements and partly unknown boundary conditions in the convection-diffusion model. The results verify that enhancing the state-space representation with the approximation error models can yield a significant improvement in the reconstructions.
Beathard, Gerald A; Spergel, Lawrence M
2013-01-01
With the rise in the median age of hemodialysis patients, the increasing numbers of patients with multiple risk factors for vascular disease, and the efforts being made to increase the creation of autogenous arteriovenous fistulas (AVFs), dialysis access-related steal syndrome (DASS) has become a growing problem. This syndrome, caused by arterial insufficiency distal to the arteriovenous access due to diversion of blood into the access, is a potentially devastating complication. It is crucial that physicians who manage hemodialysis patients and perform vascular access procedures have a comprehensive understanding of the pathophysiology, symptoms, diagnostic maneuvers, and treatment options for DASS. The goals of management must be twofold-relieve the ischemia and preserve the access. The choice of any intervention, if such is necessary, should be based upon the clinical features presented by that individual patient; the clinical condition and prognosis of the patient, stage of the disease, location of the arterial anastomosis, and the level of blood flow within the access. This review presents information that supports an individualized, physiologic approach to this condition. © 2013 Wiley Periodicals, Inc.
Space station electrical power distribution analysis using a load flow approach
NASA Technical Reports Server (NTRS)
Emanuel, Ervin M.
1987-01-01
The space station's electrical power system will evolve and grow in a manner much similar to the present terrestrial electrical power system utilities. The initial baseline reference configuration will contain more than 50 nodes or busses, inverters, transformers, overcurrent protection devices, distribution lines, solar arrays, and/or solar dynamic power generating sources. The system is designed to manage and distribute 75 KW of power single phase or three phase at 20 KHz, and grow to a level of 300 KW steady state, and must be capable of operating at a peak of 450 KW for 5 to 10 min. In order to plan far into the future and keep pace with load growth, a load flow power system analysis approach must be developed and utilized. This method is a well known energy assessment and management tool that is widely used throughout the Electrical Power Utility Industry. The results of a comprehensive evaluation and assessment of an Electrical Distribution System Analysis Program (EDSA) is discussed. Its potential use as an analysis and design tool for the 20 KHz space station electrical power system is addressed.
NASA Astrophysics Data System (ADS)
Tang, H.; Qu, K.
2014-12-01
A hybrid method that couples a geophysical fluid dynamics model to a fully 3D fluid dynamics model is the most feasible and promising approach to simulate coastal ocean flow phenomena that involve multiple types of physics spanning a vast range of temporal and spatial scales. We propose such a hybrid method that couples the Finite Volume Coastal Ocean Model (FVCOM) with the Solver for Incompressible Flow on Overset Meshes (SIFOM); the former is used to simulate large-scale estuary flows, and the latter is employed to capture small-scale local processes. The coupling involves distinct governing equations, different numerical algorithms, and dissimilar grids, and it is two-way and realized using the Schwartz alternative iteration. In this presentation, the proposed method will be outlined, and a few applications that are newly produced by it but cannot be handled by other conventional approaches will be presented.
Crowdy, Darren G; Davis, Anthony M J
2013-09-08
A transform method for determining the flow generated by the singularities of Stokes flow in a two-dimensional channel is presented. The analysis is based on a general approach to biharmonic boundary value problems in a simply connected polygon formulated by Crowdy & Fokas in this journal. The method differs from a traditional Fourier transform approach in entailing a simultaneous spectral analysis in the independent variables both along and across the channel. As an example application, we find the evolution equations for a circular treadmilling microswimmer in the channel correct to third order in the swimmer radius. Significantly, the new transform method is extendible to the analysis of Stokes flows in more complicated polygonal microchannel geometries.
Crowdy, Darren G.; Davis, Anthony M. J.
2013-01-01
A transform method for determining the flow generated by the singularities of Stokes flow in a two-dimensional channel is presented. The analysis is based on a general approach to biharmonic boundary value problems in a simply connected polygon formulated by Crowdy & Fokas in this journal. The method differs from a traditional Fourier transform approach in entailing a simultaneous spectral analysis in the independent variables both along and across the channel. As an example application, we find the evolution equations for a circular treadmilling microswimmer in the channel correct to third order in the swimmer radius. Significantly, the new transform method is extendible to the analysis of Stokes flows in more complicated polygonal microchannel geometries. PMID:24062624
John D. Armstrong; Keith H. Nislow
2012-01-01
Modelling approaches for relating discharge to the biology of Atlantic salmon, Salmo salar L., and brown trout, Salmo trutta L., growing in rivers are reviewed. Process-based and empirical models are set within a common framework of input of water flow and output of characteristics of fish, such as growth and survival, which relate directly to population dynamics. A...
NASA Astrophysics Data System (ADS)
Corsini, A.
2009-04-01
Landslide monitoring has evolved as a crucial tool in civil protection to mitigate and prevent disasters. The research presents an approach to continuous monitoring of a large-scale active earth flow using a system that integrates surface measurements obtained by a GPS and an automatic total station. With the data obtained from the system the landslide can be monitored in near-real-time and surface displacements can be directly utilized to provide early warning of slope movements and to study the behavior of the landslide, e.g. to predict timing and mechanisms of future failure. The Valoria landslide located in the northern Apennines of Italy was reactivated in 2001, 2005 and 2007 damaging roads and endangering houses. A monitoring system was installed in 2007-2008 in the frame of a civil protection plan aimed at risk mitigation. The system consists of an automatic total station measuring about 40 prisms located in the landslide to a maximum distance of 1.800 km; one double-frequency GPS receiver connects in streaming by wireless communication with 4 single-frequency GPS in side the flow. Until December 2007 the monitoring network was operated with periodic static surveying followed by the data post-processing. From September 2007 until March 2008 the landslide deformation was evaluated by periodic surveys with the total station and the GPS system. This first measure showed that the displacements were influenced by the rainfall events and by the snow melting. The total displacements measured vary from centimeter scale in the crown zone, where retrogressive movements were in progress, to over 50 m in the flow track zone. Starting in March 2008 data acquisition by the total station system and GPS were automated in order to allow continuous and near-real-time data processing. The displacement data collected in one and a half year of continuous operation show different acceleration and deceleration phases as a result of the pore water pressure distribution inside the
Hollingsworth, Jennifer A.; Palaniappan, Kumaranand; Laocharoensuk, Rawiwan; Smith, Nickolaus A.; Dickerson, Robert M.; Casson, Joanna L.; Baldwin, Jon K.
2012-06-07
Semiconductor nanowires (SC-NWs) have potential applications in diverse technologies from nanoelectronics and photonics to energy harvesting and storage due to their quantum-confined opto-electronic properties coupled with their highly anisotropic shape. Here, we explore new approaches to an important solution-based growth method known as solution-liquid-solid (SLS) growth. In SLS, molecular precursors are reacted in the presence of low-melting metal nanoparticles that serve as molten fluxes to catalyze the growth of the SC-NWs. The mechanism of growth is assumed to be similar to that of vapor-liquid-solid (VLS) growth, with the clear distinctions of being conducted in solution in the presence of coordinating ligands and at relatively lower temperatures (<300 C). The resultant SC-NWs are soluble in common organic solvents and solution processable, offering advantages such as simplified processing, scale-up, ultra-small diameters for quantum-confinement effects, and flexible choice of materials from group III-V to groups II-VI, IV-VI, as well as truly ternary I-III-VI semiconductors as we recently demonstrates. Despite these advantages of SLS growth, VLS offers several clear opportunities not allowed by conventional SLS. Namely, VLS allows sequential addition of precursors for facile synthesis of complex axial heterostructures. In addition, growth proceeds relatively slowly compared to SLS, allowing clear assessments of growth kinetics. In order to retain the materials and processing flexibility afforded by SLS, but add the elements of controlled growth afforded by VLS, we transformed SLS into a flow based method by adapting it to synthesis in a microfluidic system. By this new method - so-called 'flow-SLS' (FSLS) - we have now demonstrated unprecedented fabrication of multi-segmented SC-NWs, e.g., 8-segmented CdSe/ZnSe defined by either compositionally abrupt or alloyed interfaces as a function of growth conditions. In addition, we have studied growth rates as a
Kebede, Seifu; Admasu, Girum; Travi, Yves
2011-03-01
The isotope balance approach, which used (18)O content of waters, has been used as an independent tool to estimate inflow to Lake Tana of surface water flows from ungauged catchment of Lake Tana (50% of the total area) and evaporative water loss in the vast plains adjoining the lake. Sensitivity analysis has been conducted to investigate the effects of changes in the input parameters on the estimated flux. Surface water inflow from ungauged catchment is determined to be in the order of 1.698×10(9) m(3)a(-1). Unaccounted water loss from the lake has been estimated at 454×10(6) m(3)a(-1) (equivalent to 5% of the total via surface water). Since the lake is water tight to groundwater outflow, the major error introduced into the water balance computation is related to evaporative water loss in water from the flood plains. If drained, the water which is lost to evaporation can be used as an additional water resource for socio-economic development in the region (tourism, agriculture, hydropower, and navigation). Hydrological processes taking place in the vast flood plains of Lake Tana (origin of salinity, groundwater surface water interaction, origin of flood plain waters) have been investigated using isotopes of water and geochemistry as tracers. The salinity of shallow groundwaters in the flood plains is related to dissolution of salts accumulated in sediments covering former evaporation pools and migration of trace salt during recharge. The waters in the flood plains originate from local rainfall and river overflows and the effect of backwater flow from the lake is excluded. Minimum linkage exists between the surface waters in the flood plains and shallow groundwaters in alluvio lacustrine sediments suggesting the disappearance of flood waters following the rainy season, which is related to complete evaporation or drainage than seepage to the subsurface. There is no groundwater outflow from the lake. Inflow of groundwater cannot be ruled out. Discharge of groundwater
NASA Astrophysics Data System (ADS)
Burri, A.; Geiger, S.; Coumou, D.
2004-12-01
Many fluid-flow processes in the Earth's crust, such as multiphase flow or convection due to temperature and/or concentration gradients, are non-linear in nature. Studying these processes using numerical simulations is challenging. On one hand, numerical methods must be robust and able to deal with the non-linearities efficiently. On the other hand, they must be capable of resolving orders of magnitude variations in permeability and geologically complex structures that often occur in the Earth's subsurface. This usually requires high-resolution meshes, possibly with up to several million degrees of freedom. Traditionally numerical methods have solved such flow processes fully coupled, i.e. solving for the independent variables simultaneously using iterative techniques to account for the non-linearities. While these approaches have solved challenging problems, they have the disadvantage that the global solution matrices are ill conditioned and hence not always suitable for fast matrix solvers such as algebraic multigrid solvers. Furthermore, iterative techniques such as Newton's method may fail to converge. Numerical approaches that are capable of resolving geologically complex structures, for example the finite element method, require upwind-weighting schemes to model advection-dominated fluid flow. Such upwinding techniques, however, may reduce the geometric flexibility of the finite element method, fail to converge if the permeability varies over more than two orders of magnitude, or smear out shock fronts in advection-dominated flows. Here we present the solutions of a decoupled approach, based on a combination of finite volume and finite element methods, and a fully coupled approach, based on an upwind-weighted finite element method, for a variety of non-linear fluid flow problems. The results are compared for accuracy, robustness, and speed. They show that, in general, the decoupled approach is computationally more efficient and robust, because it does not
NASA Astrophysics Data System (ADS)
Hunt, Jason Daniel
An adaptive three-dimensional Cartesian approach for the parallel computation of compressible flow about static and dynamic configurations has been developed and validated. This is a further step towards a goal that remains elusive for CFD codes: the ability to model complex dynamic-geometry problems in a quick and automated manner. The underlying flow-solution method solves the three-dimensional Euler equations using a MUSCL-type finite-volume approach to achieve higher-order spatial accuracy. The flow solution, either steady or unsteady, is advanced in time via a two-stage time-stepping scheme. This basic solution method has been incorporated into a parallel block-adaptive Cartesian framework, using a block-octtree data structure to represent varying spatial resolution, and to compute flow solutions in parallel. The ability to represent static geometric configurations has been introduced by cutting a geometric configuration out of a background block-adaptive Cartesian grid, then solving for the flow on the resulting volume grid. This approach has been extended for dynamic geometric configurations: components of a given configuration were permitted to independently move, according to prescribed rigid-body motion. Two flow-solver difficulties arise as a result of introducing static and dynamic configurations: small time steps; and the disappearance/appearance of cell volume during a time integration step. Both of these problems have been remedied through cell merging. The concept of cell merging and its implementation within the parallel block-adaptive method is described. While the parallelization of certain grid-generation and cell-cutting routines resulted from this work, the most significant contribution was developing the novel cell-merging paradigm that was incorporated into the parallel block-adaptive framework. Lastly, example simulations both to validate the developed method and to demonstrate its full capabilities have been carried out. A simple, steady
NASA Astrophysics Data System (ADS)
Fuse, Shinichiro; Mifune, Yuto; Nakamura, Hiroyuki; Tanaka, Hiroshi
2016-11-01
Feglymycin is a naturally occurring, anti-HIV and antimicrobial 13-mer peptide that includes highly racemizable 3,5-dihydroxyphenylglycines (Dpgs). Here we describe the total synthesis of feglymycin based on a linear/convergent hybrid approach. Our originally developed micro-flow amide bond formation enabled highly racemizable peptide chain elongation based on a linear approach that was previously considered impossible. Our developed approach will enable the practical preparation of biologically active oligopeptides that contain highly racemizable amino acids, which are attractive drug candidates.
Fuse, Shinichiro; Mifune, Yuto; Nakamura, Hiroyuki; Tanaka, Hiroshi
2016-01-01
Feglymycin is a naturally occurring, anti-HIV and antimicrobial 13-mer peptide that includes highly racemizable 3,5-dihydroxyphenylglycines (Dpgs). Here we describe the total synthesis of feglymycin based on a linear/convergent hybrid approach. Our originally developed micro-flow amide bond formation enabled highly racemizable peptide chain elongation based on a linear approach that was previously considered impossible. Our developed approach will enable the practical preparation of biologically active oligopeptides that contain highly racemizable amino acids, which are attractive drug candidates. PMID:27892469
NASA Astrophysics Data System (ADS)
Fischer, Thomas; Küfmann, Carola; Haas, Florian; Baume, Otfried; Becht, Michael
2013-04-01
The high mountain systems of Central Asia (Hindukush, Pamir and Tien Shan) are dominated by continental-climatic conditions. Nevertheless, westerly maritime air circulation and convective rainfalls during the summer season result in high rainfall intensities. In combination with a high availability of unconsolidated material rainfall triggered debris flows are prominent and intensive geomorphologic processes in these mountain areas. The presented study aims to figure out a regional based modeling approach for rainfall-induced debris flow processes based on combination of a disposition model for debris flow starting zones with process-flow models. The investigation area has a size of about 700 square kilometers and is situated in the Northern Tien Shan mountains in SE Kazakhstan (investigation areas: valleys of Prochadnaja, Big Almatinka, Little Almatinka and Left Talgar). The area is characterized by mountain forest zone, alpine meadows and high-alpine glaciated areas with the highest peaks at 4500m. In a first step the disposition (point of process triggering) of actual debris flows was analyzed. Due to different triggering mechanisms, the processes were divided into channel-type and slope-type debris flows. Detailed mapping of actual debris flows initiation areas and a GIS-based geostatistical disposition analysis are used to identify the main geofactor-variables and geofactor combinations which enhance the triggering of rainfall-induced debris flows. It can be shown that both, longtime variable geofactors (such as local geomorphology and hydrology) plays a significant role for triggering debris flows, as well as mid- and short time variable geofactors. Especially actual permafrost distribution and degradation plus glacier retreat comes into the focus of interest. This is most notably for rainfall induced slope-type debris flows which primarily are triggered in the discontinuous and continuous permafrost areas eroding younger unconsolidated material from actual
Parametric distribution approach for flow availability in small hydro potential analysis
NASA Astrophysics Data System (ADS)
Abdullah, Samizee; Basri, Mohd Juhari Mat; Jamaluddin, Zahrul Zamri; Azrulhisham, Engku Ahmad; Othman, Jamel
2016-10-01
Small hydro system is one of the important sources of renewable energy and it has been recognized worldwide as clean energy sources. Small hydropower generation system uses the potential energy in flowing water to produce electricity is often questionable due to inconsistent and intermittent of power generated. Potential analysis of small hydro system which is mainly dependent on the availability of water requires the knowledge of water flow or stream flow distribution. This paper presented the possibility of applying Pearson system for stream flow availability distribution approximation in the small hydro system. By considering the stochastic nature of stream flow, the Pearson parametric distribution approximation was computed based on the significant characteristic of Pearson system applying direct correlation between the first four statistical moments of the distribution. The advantage of applying various statistical moments in small hydro potential analysis will have the ability to analyze the variation shapes of stream flow distribution.
NASA Astrophysics Data System (ADS)
Choate, J.; Tague, C.; Grant, G.
2002-12-01
In the mountainous region of the Pacific Northwest, underlying geologic and vegetation patterns, forest management practices and climate regimes at different elevations mediate the response of low flows occurring in late summer. Low-stream flow conditions, occurring during the warm, dry summers are critical to river ecosystem function and crucial to many aquatic and riparian species life cycles as well as human uses of streams. Understanding the different controls on low flow variability in this region requires a multi-scale perspective. This particular study is part of a larger strategy designed to use both empirical analysis and physically based, hydro-ecological modeling to disentangle the role that climate, geology and forest harvesting play in controlling low flows in 1st to 5th order watersheds within the Willamette basin. Our empirical analysis of summer low flow for a range of streams has shown that summer, unit-area discharge volumes are significantly lower for streams in the geologically distinct and low elevation Western Cascade versus High Cascade areas. This empirical analysis outlines large-scale regional variability. To assess and compare this with smaller scale variability, we use the RHESSys model (Regional Hydro-Ecologic Simulation System) to assess low flow behavior for small 1st order streams within the Western Cascade region. The goal is to examine low flow variability due to both climate and forest harvesting and recovery and place this in the context of regional scale analysis. We use multiple simulations to predict low flow volumes under cut and uncut conditions for wet/dry and warm/cool climate scenarios. Future work will replicate this study to examine 1st order watershed sensitivity within the contrasting High Cascade geologic region. The combined multi-scale empirical and modeling approach will then be used to provide a more comprehensive assessment of low flow patterns and sensitivity within this region.
Acute Portal Hypertension Models in Dogs: Low- and High-Flow Approaches
Dave, Jaydev K; Liu, Ji-Bin; Halldorsdottir, Valgerdur G; Eisenbrey, John R; Merton, Daniel A; Machado, Priscilla; Zhao, Hongjia; Altemus, Joseph; Needleman, Laurence; Brown, Daniel B; Forsberg, Flemming
2012-01-01
Effective animal models are needed to evaluate the feasibility of new techniques to assess portal hypertension (PH). Here we developed 2 canine models of acute PH by increasing intrasinusoidal resistance and by increasing the portal vein (PV) flow volume to test the efficacy of a noninvasive technique to evaluate PH. The acute low-flow PH model was based on embolization of liver circulation by using a gelatin sponge material. The acute high-flow PH model was based on increasing the PV flow volume by using an arteriovenous (A-V) shunt from the femoral artery and saline infusion. PV pressures and diameters were assessed before and after inducing PH. Pressure values and diameters were obtained from the inferior vena cava in 3 unmanipulated controls. The low-flow model of PH was repeatable and successfully increased PV pressure by an average of 16.5 mm Hg within 15 min. The high-flow model of PH failed to achieve increased PV pressures. However, saline supplementation of the portal circulation in the high-flow model led to mean increases in PV pressures of 12.8 mm Hg within 20 min. Pulsatility in the PV was decreased in the low-flow model and increased in the high-flow model relative to baseline. No changes in PV diameter were noted in either model. These acute PH models are relatively straightforward to implement and may facilitate the evaluation of new techniques to assess PH. PMID:23114046
Fluidelastic instability in a confined annular flow: An experimental and analytical approach
Porcher, G.; Langre, E. de
1996-12-01
Self excitation of slender structures under axial flow have been reported in a large variety of local flow configurations. This paper reports the result of a research program, both experimental and analytical, aimed at the result of the basic phenomena leading to such instabilities. A cylindrical body with a diffuser is put in a confined annular flow of water. A case of flutter is observed and analyzed with a classical potential flow method and with a friction based model. Closed-form solutions are proposed and the origin of the flutter instability is discussed. This is relevant for nuclear fuel studies.
Acute portal hypertension models in dogs: low- and high-flow approaches.
Dave, Jaydev K; Liu, Ji-Bin; Halldorsdottir, Valgerdur G; Eisenbrey, John R; Merton, Daniel A; Machado, Priscilla; Zhao, Hongjia; Altemus, Joseph; Needleman, Laurence; Brown, Daniel B; Forsberg, Flemming
2012-10-01
Effective animal models are needed to evaluate the feasibility of new techniques to assess portal hypertension (PH). Here we developed 2 canine models of acute PH by increasing intrasinusoidal resistance and by increasing the portal vein (PV) flow volume to test the efficacy of a noninvasive technique to evaluate PH. The acute low-flow PH model was based on embolization of liver circulation by using a gelatin sponge material. The acute high-flow PH model was based on increasing the PV flow volume by using an arteriovenous (A-V) shunt from the femoral artery and saline infusion. PV pressures and diameters were assessed before and after inducing PH. Pressure values and diameters were obtained from the inferior vena cava in 3 unmanipulated controls. The low-flow model of PH was repeatable and successfully increased PV pressure by an average of 16.5 mm Hg within 15 min. The high-flow model of PH failed to achieve increased PV pressures. However, saline supplementation of the portal circulation in the high-flow model led to mean increases in PV pressures of 12.8 mm Hg within 20 min. Pulsatility in the PV was decreased in the low-flow model and increased in the high-flow model relative to baseline. No changes in PV diameter were noted in either model. These acute PH models are relatively straightforward to implement and may facilitate the evaluation of new techniques to assess PH.
Huang, D; Chernyshenko, S; Goulart, P; Lasagna, D; Tutty, O; Fuentes, F
2015-11-08
With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier-Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach.
Tutty, O.
2015-01-01
With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier–Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach. PMID:26730219
Itu, Lucian; Rapaka, Saikiran; Passerini, Tiziano; Georgescu, Bogdan; Schwemmer, Chris; Schoebinger, Max; Flohr, Thomas; Sharma, Puneet; Comaniciu, Dorin
2016-07-01
Fractional flow reserve (FFR) is a functional index quantifying the severity of coronary artery lesions and is clinically obtained using an invasive, catheter-based measurement. Recently, physics-based models have shown great promise in being able to noninvasively estimate FFR from patient-specific anatomical information, e.g., obtained from computed tomography scans of the heart and the coronary arteries. However, these models have high computational demand, limiting their clinical adoption. In this paper, we present a machine-learning-based model for predicting FFR as an alternative to physics-based approaches. The model is trained on a large database of synthetically generated coronary anatomies, where the target values are computed using the physics-based model. The trained model predicts FFR at each point along the centerline of the coronary tree, and its performance was assessed by comparing the predictions against physics-based computations and against invasively measured FFR for 87 patients and 125 lesions in total. Correlation between machine-learning and physics-based predictions was excellent (0.9994, P < 0.001), and no systematic bias was found in Bland-Altman analysis: mean difference was -0.00081 ± 0.0039. Invasive FFR ≤ 0.80 was found in 38 lesions out of 125 and was predicted by the machine-learning algorithm with a sensitivity of 81.6%, a specificity of 83.9%, and an accuracy of 83.2%. The correlation was 0.729 (P < 0.001). Compared with the physics-based computation, average execution time was reduced by more than 80 times, leading to near real-time assessment of FFR. Average execution time went down from 196.3 ± 78.5 s for the CFD model to ∼2.4 ± 0.44 s for the machine-learning model on a workstation with 3.4-GHz Intel i7 8-core processor.
Approaches to Modeling Coupled Flow and Reaction in a 2-D Cementation Experiment
Steefel, Carl; Cochepin, B.; Trotignon, L.; Bildstein, O.; Steefel, C.; Lagneau, V.; van der Lee, J.
2008-04-01
Porosity evolution at reactive interfaces is a key process that governs the evolution and performances of many engineered systems that have important applications in earth and environmental sciences. This is the case, for example, at the interface between cement structures and clays in deep geological nuclear waste disposals. Although in a different transport regime, similar questions arise for permeable reactive barriers used for biogeochemical remediation in surface environments. The COMEDIE project aims at investigating the coupling between transport, hydrodynamics and chemistry when significant variations of porosity occur. The present work focuses on a numerical benchmark used as a design exercise for the future COMEDIE-2D experiment. The use of reactive transport simulation tools like Hytec and Crunch provides predictions of the physico-chemical evolutions that are expected during the future experiments in laboratory. Focus is given in this paper on the evolution during the simulated experiment of precipitate, permeability and porosity fields. A first case is considered in which the porosity is constant. Results obtained with Crunch and Hytec are in relatively good agreement. Differences are attributable to the models of reactive surface area taken into account for dissolution/precipitation processes. Crunch and Hytec simulations taking into account porosity variations are then presented and compared. Results given by the two codes are in qualitative agreement, with differences attributable in part to the models of reactive surface area for dissolution/precipitation processes. As a consequence, the localization of secondary precipitates predicted by Crunch leads to lower local porosities than for predictions obtained by Hytec and thus to a stronger coupling between flow and chemistry. This benchmark highlights the importance of the surface area model employed to describe systems in which strong porosity variations occur as a result of dissolution
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Liu, Nan-Suey
2008-01-01
This paper describes an approach which aims at bridging the gap between the traditional Reynolds-averaged Navier-Stokes (RANS) approach and the traditional large eddy simulation (LES) approach. It has the characteristics of the very large eddy simulation (VLES) and we call this approach the partially-resolved numerical simulation (PRNS). Systematic simulations using the National Combustion Code (NCC) have been carried out for fully developed turbulent pipe flows at different Reynolds numbers to evaluate the PRNS approach. Also presented are the sample results of two demonstration cases: nonreacting flow in a single injector flame tube and reacting flow in a Lean Direct Injection (LDI) hydrogen combustor.
Gaston, L.; Glut, B.; Bellet, M.; Chenot, J.L.
1995-12-31
This paper presents a two-dimensional lagrangian-eulerian finite element approach of non-steady state Navier-Stokes fluid flows with free surfaces, like those occurring during the mould filling stage in casting processes. The proposed model is based on a mixed velocity-pressure finite element formulation, including an augmented Lagrangian technique and an iterative solver of Uzawa type. Mesh updating is carried out through an arbitrary lagrangian-eulerian method in order to describe properly the free surface evolution. Heat transfer through the fluid flow is solved by a convection-diffusion splitting technique. The efficiency of the method is illustrated on an example of gravity casting.
NASA Astrophysics Data System (ADS)
Gogoi, Bidyut B.
2016-07-01
We have recently analyzed the global two-dimensional (2D) stability of the staggered lid-driven cavity (LDC) flow with a higher order compact (HOC) approach. In the analysis, critical parameters are determined for both the parallel and anti-parallel motion of the lids and a detailed analysis has been carried out on either side of the critical values. In this article, we carry out an investigation of flow stabilities inside a two-sided cross lid-driven cavity with a pair of opposite lids moving in both parallel and anti-parallel directions. On discretization, the governing 2D Navier-Stokes (N-S) equations describing the steady flow and flow perturbations results in a generalized eigenvalue problem which is solved for determining the critical parameters on four different grids. Elaborate computation is performed for a wide range of Reynolds numbers (Re) on either side of the critical values in the range 200 ⩽ Re ⩽ 10000. For flows below the critical Reynolds number Rec, our numerical results are compared with established steady-state results and excellent agreement is obtained in all the cases. For Reynolds numbers above Rec, phase plane and spectral density analysis confirmed the existence of periodic, quasi-periodic, and stable flow patterns.
NASA Technical Reports Server (NTRS)
Hafez, M.; Soliman, M.; White, S.
1992-01-01
A new formulation (including the choice of variables, their non-dimensionalization, and the form of the artificial viscosity) is proposed for the numerical solution of the full Navier-Stokes equations for compressible and incompressible flows with heat transfer. With the present approach, the same code can be used for constant as well as variable density flows. The changes of the density due to pressure and temperature variations are identified and it is shown that the low Mach number approximation is a special case. At zero Mach number, the density changes due to the temperature variation are accounted for, mainly through a body force term in the momentum equation. It is also shown that the Boussinesq approximation of the buoyancy effects in an incompressible flow is a special case. To demonstrate the new capability, three examples are tested. Flows in driven cavities with adiabatic and isothermal walls are simulated with the same code as well as incompressible and supersonic flows over a wall with and without a groove. Finally, viscous flow simulations of an oblique shock reflection from a flat plate are shown to be in good agreement with the solutions available in literature.
The Current Status of Unsteady CFD Approaches for Aerodynamic Flow Control
NASA Technical Reports Server (NTRS)
Carpenter, Mark H.; Singer, Bart A.; Yamaleev, Nail; Vatsa, Veer N.; Viken, Sally A.; Atkins, Harold L.
2002-01-01
An overview of the current status of time dependent algorithms is presented. Special attention is given to algorithms used to predict fluid actuator flows, as well as other active and passive flow control devices. Capabilities for the next decade are predicted, and principal impediments to the progress of time-dependent algorithms are identified.
NASA Astrophysics Data System (ADS)
Margaris, Konstantinos N.; Nepiyushchikh, Zhanna; Zawieja, David C.; Moore, James; Black, Richard A.
2016-02-01
We describe the development of an optical flow visualization method for resolving the flow velocity vector field in lymphatic vessels in vitro. The aim is to develop an experimental protocol for accurately estimating flow parameters, such as flow rate and shear stresses, with high spatial and temporal resolution. Previous studies in situ have relied on lymphocytes as tracers, but their low density resulted in a reduced spatial resolution whereas the assumption that the flow was fully developed in order to determine the flow parameters of interest may not be valid, especially in the vicinity of the valves, where the flow is undoubtedly more complex. To overcome these issues, we have applied the time-resolved microparticle image velocimetry (μ-PIV) technique, a well-established method that can provide increased spatial and temporal resolution that this transient flow demands. To that end, we have developed a custom light source, utilizing high-power light-emitting diodes, and associated control and image processing software. This paper reports the performance of the system and the results of a series of preliminary experiments performed on vessels isolated from rat mesenteries, demonstrating, for the first time, the successful application of the μ-PIV technique in these vessels.
Margaris, Konstantinos N; Nepiyushchikh, Zhanna; Zawieja, David C; Moore, James; Black, Richard A
2016-02-01
We describe the development of an optical flow visualization method for resolving the flow velocity vector field in lymphatic vessels in vitro. The aim is to develop an experimental protocol for accurately estimating flow parameters, such as flow rate and shear stresses, with high spatial and temporal resolution. Previous studies in situ have relied on lymphocytes as tracers, but their low density resulted in a reduced spatial resolution whereas the assumption that the flow was fully developed in order to determine the flow parameters of interest may not be valid, especially in the vicinity of the valves, where the flow is undoubtedly more complex. To overcome these issues, we have applied the time-resolved microparticle image velocimetry (μ -PIV) technique, a well-established method that can provide increased spatial and temporal resolution that this transient flow demands. To that end, we have developed a custom light source, utilizing high-power light-emitting diodes, and associated control and image processing software. This paper reports the performance of the system and the results of a series of preliminary experiments performed on vessels isolated from rat mesenteries, demonstrating, for the first time, the successful application of the μ -PIV technique in these vessels.
H.R. Barnard; C.B. Graham; W.J. van Verseveld; J.R. Brooks; B.J. Bond; J.J. McDonnell
2010-01-01
Mechanistic assessment of how transpiration influences subsurface flow is necessary to advance understanding of catchment hydrology. We conducted a 24-day, steady-state irrigation experiment to quantify the relationships among soil moisture, transpiration and hillslope subsurface flow. Our objectives were to: (1) examine the time lag between maximum transpiration and...
ERIC Educational Resources Information Center
Young, Michael E.; Haight, Michael J.
An analytic system for colleges that involves student flow calculation, an historical curriculum matrix, and departmental workload forecasts is examined. The conceptual base, uses of the data, technical issues, and implementation are covered. The student flow calculation uses enrollment trends to develop the probability of a student with a given…
MODELING AIR FLOW DYNAMICS IN RADON MITIGATION SYSTEMS: A SIMPLIFIED APPROACH
The paper refines and extends an earlier study--relating to the design of optimal radon mitigation systems based on subslab depressurization-- that suggested that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained betw...
MODELING AIR FLOW DYNAMICS IN RADON MITIGATION SYSTEMS: A SIMPLIFIED APPROACH
The paper refines and extends an earlier study--relating to the design of optimal radon mitigation systems based on subslab depressurization-- that suggested that subslab air flow induced by a central suction point be treated as radial air flow through a porous bed contained betw...
NASA Astrophysics Data System (ADS)
Yang, Jun; Chu, Xuefeng
2015-04-01
Realistic modeling of discontinuous overland flow on irregular topographic surfaces has been proven to be a challenge. This study is aimed to develop a new modeling framework to simulate the discontinuous puddle-to-puddle (P2P) overland flow dynamics for infiltrating surfaces with various microtopographic characteristics. In the P2P model, puddles were integrated in a well-delineated, cascaded drainage system to facilitate explicit simulation of their dynamic behaviors and interactions. Overland flow and infiltration were respectively simulated by using the diffusion wave model and a modified Green-Ampt model for the DEM-derived flow drainage network that consisted of a series of puddle-based units (PBUs). The P2P model was tested by using a series of data from laboratory overland flow experiments for various microtopography, soil, and rainfall conditions. The modeling results indicated that the hierarchical relationships and microtopographic properties of puddles significantly affected their connectivity, filling-spilling dynamics, and the associated threshold flow. Surface microtopography and rainfall characteristics also exhibited strong influences on the spatio-temporal distributions of infiltration rates, runoff fluxes, and unsaturated flow. The model tests demonstrated its applicability in simulating microtopography-dominated overland flow on infiltrating surfaces.
Sonenshein, R.S.
1995-01-01
A hydrogeologic approach that integrates the use of hydrogeologic and spatial tools aids in the identification of land uses that overlie ground- water flow paths and permits a better understanding of ground-water flow systems. A mathematical model was used to simulate the ground-water flow system in Broward County, particle-tracking software was used to determine flow paths leading to the monitor wells in Broward County, and a Geographic Information System was used to identify which land uses overlie the flow paths. A procedure using a geographic information system to evaluate the output from a ground-water flow model has been documented. The ground-water flow model was used to represent steady-state conditions during selected wet- and dry-season months, and an advective flow particle- tracking program was used to simulate the direction of ground-water flow in the aquifer system. Digital spatial data layers were created from the particle pathlines that lead to the vicinity of the open interval of selected wells in the Broward County ground-water quality monitoring network. Buffer zone data layers were created, surrounding the particle pathlines to represent the area of contribution to the water sampled from the monitor wells. Spatial data layers, combined with a land-use data layer, were used to identify the land uses that overlie the ground-water flow paths leading to the monitor wells. The simulation analysis was performed on five Broward County wells with different hydraulic parameters to determine the source of ground-water stress, determine selected particle pathlines, and identify land use in buffer zones in the vicinity of the wells. The flow paths that lead to the grid cells containing wells G-2355, G-2373, and G-2373A did not vary between the wet- and dry-season conditions. Changes in the area of contribution for wells G-2345X and G-2369 were attributed to variations in rainfall patterns, well-field pumpage, and surface-water management practices
NASA Astrophysics Data System (ADS)
Koppol, Anantha Padmanabha Rao
Flows of viscoelastic polymeric fluids are of great fundamental and practical interest as polymeric materials for commodity and value-added products are processed typically in a fluid state. The nonlinear coupling between fluid motion and microstructure, which results in highly non-Newtonian theology, memory/relaxation and normal stress development or tension along streamlines, greatly complicates the analysis, design and control of such flows. This has posed tremendous challenges to researchers engaged in developing first principles models and simulations that can accurately and robustly predict the dynamical behavior of polymeric flows. Despite this, the past two decades have witnessed several significant advances towards accomplishing this goal. Yet a problem of fundamental and great pragmatic interest has defied solution to years of ardent research by several groups, namely the relationship between friction drag and flow rate in inertialess flows of highly elastic polymer solutions in complex kinematics flows. First principles-based solution of this long-standing problem in non-Newtonian fluid mechanics is the goal of this research. To achieve our objective, it is essential to develop the capability to perform large-scale multiscale simulations, which integrate continuum-level finite element solvers for the conservation of mass and momentum with fast integrators of stochastic differential equations that describe the evolution of polymer configuration. Hence, in this research we have focused our attention on development of a parallel, multiscale simulation algorithm that is capable of robustly and efficiently simulating complex kinematics flows of dilute polymeric solutions using the first principles based bead-spring chain description of the polymer molecules. The fidelity and computational efficiency of the algorithm has been demonstrated via three benchmark flow problems, namely, the plane Couette flow, the Poiseuille flow and the 4:1:4 axisymmetric
The unified power flow controller: A new approach to power transmission control
Gyugyi, L.; Schauder, C.D.; Williams, S.L.; Rietman, T.R.; Torgerson, D.R.; Edris, A.
1995-04-01
This paper shows that the Unified Power Flow Controller (UPFC) is able to control both the transmitted real power and, independently, the reactive power flows at the sending-and the receiving-end of the transmission line. The unique capabilities of the UPFC in multiple line compensation are integrated into a generalized power flow controller that is able to maintain prescribed, and independently controllable, real power and reactive power flow in the line. The paper describes the basic concepts of the proposed generalized P and Q controller and compares it to the more conventional, but related power flow controller, such as the Thyristor-Controlled Series Capacitor and Thyristor-Controlled Phase Angle Regulator. The paper also presents results of computer simulations showing the performance of the UPFC under different system conditions.
An Approach for Assessing Turbulent Flow Damage to Blood in Medical Devices.
Ozturk, Mesude; Papavassiliou, Dimitrios V; O'Rear, Edgar A
2017-01-01
In this work, contributing factors for red blood cell (RBC) damage in turbulence are investigated by simulating jet flow experiments. Results show that dissipative eddies comparable or smaller in size to the red blood cells cause hemolysis and that hemolysis corresponds to the number and, more importantly, the surface area of eddies that are associated with Kolmogorov length scale (KLS) smaller than about 10 μm. The size distribution of Kolmogorov scale eddies is used to define a turbulent flow extensive property with eddies serving as a means to assess the turbulence effectiveness in damaging cells, and a new hemolysis model is proposed. This empirical model is in agreement with hemolysis results for well-defined systems that exhibit different exposure times and flow conditions, in Couette flow viscometer, capillary tube, and jet flow experiments.
NASA Astrophysics Data System (ADS)
Cronkite-Ratcliff, C.; Phelps, G. A.; Boucher, A.
2011-12-01
In many geologic settings, the pathways of groundwater flow are controlled by geologic heterogeneities which have complex geometries. Models of these geologic heterogeneities, and consequently, their effects on the simulated pathways of groundwater flow, are characterized by uncertainty. Multiple-point geostatistics, which uses a training image to represent complex geometric descriptions of geologic heterogeneity, provides a stochastic approach to the analysis of geologic uncertainty. Incorporating multiple-point geostatistics into numerical models provides a way to extend this analysis to the effects of geologic uncertainty on the results of flow simulations. We present two case studies to demonstrate the application of multiple-point geostatistics to numerical flow simulation in complex geologic settings with both static and dynamic conditioning data. Both cases involve the development of a training image from a complex geometric description of the geologic environment. Geologic heterogeneity is modeled stochastically by generating multiple equally-probable realizations, all consistent with the training image. Numerical flow simulation for each stochastic realization provides the basis for analyzing the effects of geologic uncertainty on simulated hydraulic response. The first case study is a hypothetical geologic scenario developed using data from the alluvial deposits in Yucca Flat, Nevada. The SNESIM algorithm is used to stochastically model geologic heterogeneity conditioned to the mapped surface geology as well as vertical drill-hole data. Numerical simulation of groundwater flow and contaminant transport through geologic models produces a distribution of hydraulic responses and contaminant concentration results. From this distribution of results, the probability of exceeding a given contaminant concentration threshold can be used as an indicator of uncertainty about the location of the contaminant plume boundary. The second case study considers a
Tardiole Kuehne, Bruno; Estrella, Julio Cezar; Nunes, Luiz Henrique; Martins de Oliveira, Edvard; Hideo Nakamura, Luis; Gomes Ferreira, Carlos Henrique; Carlucci Santana, Regina Helena; Reiff-Marganiec, Stephan; Santana, Marcos José
2015-01-01
This paper proposes a system named AWSCS (Automatic Web Service Composition System) to evaluate different approaches for automatic composition of Web services, based on QoS parameters that are measured at execution time. The AWSCS is a system to implement different approaches for automatic composition of Web services and also to execute the resulting flows from these approaches. Aiming at demonstrating the results of this paper, a scenario was developed, where empirical flows were built to demonstrate the operation of AWSCS, since algorithms for automatic composition are not readily available to test. The results allow us to study the behaviour of running composite Web services, when flows with the same functionality but different problem-solving strategies were compared. Furthermore, we observed that the influence of the load applied on the running system as the type of load submitted to the system is an important factor to define which approach for the Web service composition can achieve the best performance in production. PMID:26068216
NASA Astrophysics Data System (ADS)
Kaspi, Y.; Davighi, J. E.; Galanti, E.; Hubbard, W. B.
2016-09-01
The upcoming Juno and Cassini gravity measurements of Jupiter and Saturn, respectively, will allow probing the internal dynamics of these planets through accurate analysis of their gravity spectra. To date, two general approaches have been suggested for relating the flow velocities and gravity fields. In the first, barotropic potential surface models, which naturally take into account the oblateness of the planet, are used to calculate the gravity field. However, barotropicity restricts the flows to be constant along cylinders parallel to the rotation axis. The second approach, calculated in the reference frame of the rotating planet, assumes that due to the large scale and rapid rotation of these planets, the winds are to leading order in geostrophic balance. Therefore, thermal wind balance relates the wind shear to the density gradients. While this approach can take into account any internal flow structure, it is limited to only calculating the dynamical gravity contributions, and has traditionally assumed spherical symmetry. This study comes to relate the two approaches both from a theoretical perspective, showing that they are analytically identical in the barotropic limit, and numerically, through systematically comparing the different model solutions for the gravity harmonics. For the barotropic potential surface models we employ two independent solution methods - the potential-theory and Maclaurin spheroid methods. We find that despite the sphericity assumption, in the barotropic limit the thermal wind solutions match well the barotropic oblate potential-surface solutions.
A combined experimental-numerical approach for two-phase flow boiling in a minichannel
NASA Astrophysics Data System (ADS)
Hożejowska, Sylwia; Grabowski, Mirosław
2016-03-01
The paper addresses experimental and numerical modeling of the two-phase flows in an asymmetrically heated horizontal minichannel. Experimental measurements concerned flows of evaporating ethanol in a minichannel with rectangular cross section 1.8mm × 2 mm. In order to observe the flows, measuring system was designed and built. The system measured and recorded basic heat and flow parameters of flowing fluid, and the temperature of external surface of the heater by using infrared camera and recorded images of flow with high-speed camera. The second aim of the paper was to formulate appropriate flow boiling heat transfer model, which would minimises the use of experimentally determined constants. The procedure of calculating the temperature of the ethanol is coupled with concurrent process of determining the temperature distributions in the isolating foil and the heating surface. The two-dimensional temperature distributions in three subsequent domains were calculated with Trefftz method. Due to the Robin condition, heat transfer coefficient at the heating surface-ethanol interface was calculated based on the known temperature distributions of the foil and liquid. Additionally, the paper describes the relation between two sets of functions used in the calculation. Numerical calculations made by Trefftz method were performed with using experimental data.
Deposition and fine particle production during dynamic flow in a dry powder inhaler: a CFD approach.
Milenkovic, J; Alexopoulos, A H; Kiparissides, C
2014-01-30
In this work the dynamic flow as well as the particle motion and deposition in a commercial dry powder inhaler, DPI (i.e., Turbuhaler) is described using computational fluid dynamics, CFD. The dynamic flow model presented here is an extension of a steady flow model previously described in Milenkovic et al. (2013). The model integrates CFD simulations for dynamic flow, an Eulerian-fluid/Lagrangian-particle description of particle motion as well as a particle/wall interaction model providing the sticking efficiency of particles colliding with the DPI walls. The dynamic flow is imposed by a time varying outlet pressure and the particle injections into the DPI are assumed to occur instantaneously and follow a prescribed particle size distribution, PSD. The total particle deposition and the production of fine particles in the DPI are determined for different peak inspiratory flow rates, PIFR, flow increase rates, FIR, and particle injection times. The simulation results for particle deposition are found to agree well with available experimental data for different values of PIFR and FIR. The predicted values of fine particle fraction are in agreement with available experimental results when the mean size of the injected PSD is taken to depend on the PIFR. Copyright © 2013 Elsevier B.V. All rights reserved.
Kierkegaard, Axel; Boij, Susann; Efraimsson, Gunilla
2010-02-01
Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier-Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier-Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.
NASA Astrophysics Data System (ADS)
Redapangu, Prasanna R.; Sahu, Kirti Chandra; Vanka, S. P.
2013-11-01
A three-dimensional multiphase lattice Boltzmann approach is used to study the pressure-driven displacement flow of two immiscible liquids of different densities and viscosities in an inclined square duct. A three-dimensional-fifteen-velocity (D3Q15) lattice model is used. The simulations are performed on a graphics processing unit (GPU) based machine. The effects of channel inclination, viscosity and density contrasts are investigated. The contours of the density and the average viscosity profiles in different planes are plotted and compared with two dimensional simulations. We demonstrate that the flow dynamics in three-dimensional channel is quite different as compared to that of two-dimensional channel. In particular, we found that the flow is relatively more coherent in three-dimensional channel than that in two-dimensional channel. A new screw-type instability is seen in the three-dimensional channel which cannot be observed in two-dimensional simulations.
Ötvös, Sándor B; Mándity, István M; Fülöp, Ferenc
2011-08-01
A simple and efficient flow-based technique is reported for the catalytic deuteration of several model nitrogen-containing heterocyclic compounds which are important building blocks of pharmacologically active materials. A continuous flow reactor was used in combination with on-demand pressure-controlled electrolytic D(2) production. The D(2) source was D(2)O, the consumption of which was very low. The experimental set-up allows the fine-tuning of pressure, temperature, and flow rate so as to determine the optimal conditions for the deuteration reactions. The described procedure lacks most of the drawbacks of the conventional batch deuteration techniques, and additionally is highly selective and reproducible.
NASA Astrophysics Data System (ADS)
Stanko, Z.; Boyce, S. E.; Yeh, W. W. G.
2015-12-01
Model reduction techniques using proper orthogonal decomposition (POD) have been very effective in applications to confined groundwater flow models. These techniques consist of performing a projection of the solution of the full model onto a reduced basis. POD combined with the snapshot approach has been successfully applied to highly discretized linear models. In many cases, the reduced model is orders of magnitude smaller than the full model and runs 1,000 times faster. For nonlinear models, such as the unconfined groundwater flow, direct application of POD requires additional calls to the full model to generate additional snapshots. This is time consuming and increases the dimension of the reduced model. The discrete empirical interpolation method (DEIM) is a technique that avoids the additional full model calls and captures the dynamics of the nonlinear term while reducing the dimensions. Here, POD and DEIM are combined to reduce both the nonlinear unconfined groundwater flow and solute transport equations. To prove the concept, simple one-dimensional models are created for MODFLOW and MT3DMS separately. The dual approach is then tested on a density-dependent flow and transport simulation using the LMT package developed for MODFLOW. For each iteration of the nonlinear flow solver and the transport solver, the respective reduced models are solved instead. Numerical experiments show that significant reduction is obtainable before errors become too large. This method is well suited for a coastal aquifer seawater intrusion scenario, where nonlinearities only exist in small subregions of the model domain. A fine discretization can be utilized and POD will effectively eliminate unnecessary parameterization by projecting the full model system matrix onto a subspace with fewer column dimensions. DEIM can then reduce the row dimension of the original system by using only those state variable nodes with the most influence. This combined approach allows for full
LPMLE3: A novel 1-D approach to study water flow in streambeds using heat as a tracer
NASA Astrophysics Data System (ADS)
Schneidewind, U.; van Berkel, M.; Anibas, C.; Vandersteen, G.; Schmidt, C.; Joris, I.; Seuntjens, P.; Batelaan, O.; Zwart, H. J.
2016-08-01
We introduce LPMLE3, a new 1-D approach to quantify vertical water flow components at streambeds using temperature data collected in different depths. LPMLE3 solves the partial differential equation for coupled water flow and heat transport in the frequency domain. Unlike other 1-D approaches it does not assume a semi-infinite halfspace with the location of the lower boundary condition approaching infinity. Instead, it uses local upper and lower boundary conditions. As such, the streambed can be divided into finite subdomains bound at the top and bottom by a temperature-time series. Information from a third temperature sensor within each subdomain is then used for parameter estimation. LPMLE3 applies a low order local polynomial to separate periodic and transient parts (including the noise contributions) of a temperature-time series and calculates the frequency response of each subdomain to a known temperature input at the streambed top. A maximum-likelihood estimator is used to estimate the vertical component of water flow, thermal diffusivity, and their uncertainties for each streambed subdomain and provides information regarding model quality. We tested the method on synthetic temperature data generated with the numerical model STRIVE and demonstrate how the vertical flow component can be quantified for field data collected in a Belgian stream. We show that by using the results in additional analyses, nonvertical flow components could be identified and by making certain assumptions they could be quantified for each subdomain. LPMLE3 performed well on both simulated and field data and can be considered a valuable addition to the existing 1-D methods.
A Renormalization-Group Approach of the Up-Scaling Problem of Flow in Heterogeneous Porous Media
NASA Astrophysics Data System (ADS)
noetinger, B.
2001-12-01
Powerful methods coming from statistical physics are becoming increasingly popular to get a faithful theoretical description of flow and transport in heterogeneous aquifers that are described by mean of geostatistics. However,in current practice people still use Monte Carlo simulations that are well suited to account for complex boundaries and flow patterns. Here, we present an approach intending to up-scale directly the geostatistical description rather than realization by realization as usual. It is based upon a renormalization group analysis close in spirit with previous works and P King and Jaekel and Vereecken. Using a so called "weak approximation"(Neuman and Orr) , we obtain differential equations driving the permeability variogram parameters as a function of the wave-vector cut-off smoothing the permeability maps. At the end of the process, in the isotropic case, the Landau Lifshitz Matheron conjecture is recovered. This conjecture appears thus as being a consequence of both renormalization approach and the weak approximation. The approach is currently being generalized to anisotropic media. These results can be used to perform cheaper Monte Carlo simulations at a coarser scale. P. King, The Use of Field Theoretic Methods for the Study of Flow in Heterogeneous Porous Medium", J. Phys. A.: Math. Gen. 20, pp3935-3947,1987 U. Jaekel and H. Vereecken, Renormalization Group Analysis of Macrodispersion in a Directed Random Flow, Water Resources Research,33,10,pp 2287-2299, 1997 Neuman, S.P. and Orr, S. "Prediction of Steady State Flow in Nonuniform Geologic Media by Conditional Moments: Exact non local Formalism, Effective Conductivities and Weak Approximation", Water Resources Research 29 (2)341-364 (1993) Noetinger, B. Computing the Effective Permeability of log-normal permeability fields using renormalization methods. C.R . Acad. Des Sciences,Sciences de la Terre et des Planètes, 331 353-357 (2000)
A unified approach to fluid-flow, geomechanical, and seismic modelling
NASA Astrophysics Data System (ADS)
Yarushina, Viktoriya; Minakov, Alexander
2016-04-01
The perturbations of pore pressure can generate seismicity. This is supported by observations from human activities that involve fluid injection into rocks at high pressure (hydraulic fracturing, CO2 storage, geothermal energy production) and natural examples such as volcanic earthquakes. Although the seismic signals that emerge during geotechnical operations are small both in amplitude and duration when compared to natural counterparts. A possible explanation for the earthquake source mechanism is based on a number of in situ stress measurements suggesting that the crustal rocks are close to its plastic yield limit. Hence, a rapid increase of the pore pressure decreases the effective normal stress, and, thus, can trigger seismic shear deformation. At the same time, little attention has been paid to the fact that the perturbation of fluid pressure itself represents an acoustic source. Moreover, non-double-couple source mechanisms are frequently reported from the analysis of microseismicity. A consistent formulation of the source mechanism describing microseismic events should include both a shear and isotropic component. Thus, improved understanding of the interaction between fluid flow and seismic deformation is needed. With this study we aim to increase the competence in integrating real-time microseismic monitoring with geomechanical modelling such that there is a feedback loop between monitored deformation and stress field modelling. We propose fully integrated seismic, geomechanical and reservoir modelling. Our mathematical formulation is based on fundamental set of force balance, mass balance, and constitutive poro-elastoplastic equations for two-phase media consisting of deformable solid rock frame and viscous fluid. We consider a simplified 1D modelling setup for consistent acoustic source and wave propagation in poro-elastoplastic media. In this formulation the seismic wave is generated due to local changes of the stress field and pore pressure induced by
NASA Astrophysics Data System (ADS)
de Castro, Marcelo Souza; Rodriguez, Oscar Mauricio Hernandez
2016-06-01
The study of the hydrodynamic stability of flow patterns is important in the design of equipment and pipelines for multiphase flows. The maintenance of a particular flow pattern becomes important in many applications, e.g., stratified flow pattern in heavy oil production avoiding the formation of emulsions because of the separation of phases and annular flow pattern in heat exchangers which increases the heat transfer coefficient. Flow maps are drawn to orientate engineers which flow pattern is present in a pipeline, for example. The ways how these flow maps are drawn have changed from totally experimental work, to phenomenological models, and then to stability analysis theories. In this work an experimental liquid-liquid flow map, with water and viscous oil as work fluids, drawn via subjective approach with high speed camera was used to compare to approaches of the same theory: the interfacial-tension-force model. This theory was used to drawn the wavy stratified flow pattern transition boundary. This paper presents a comparison between the two approaches of the interfacial-tension-force model for transition boundaries of liquid-liquid flow patterns: (i) solving the wave equation for the wave speed and using average values for wave number and wave speed; and (ii) solving the same equation for the wave number and then using a correlation for the wave speed. The results show that the second approach presents better results.
NASA Astrophysics Data System (ADS)
Comte, J.-C.; Wilson, C.; Ofterdinger, U.; González-Quirós, A.
2017-03-01
Volcanic dykes are common discrete heterogeneities in aquifers; however, there is a lack of field examples of, and methodologies for, comprehensive in situ characterization of their properties with respect to groundwater flow and solute transport. We have applied an integrated multiphysics approach to quantify the effect of dolerite dykes on saltwater intrusion in a coastal sandstone aquifer. The approach involved ground geophysical imaging (passive magnetics and electrical resistivity tomography), well hydraulic testing, and tidal propagation analysis, which provided constraints on the geometry of the dyke network, the subsurface saltwater distribution, and the sandstone hydrodynamic properties and connectivity. A three-dimensional variable-density groundwater model coupled with a resistivity model was further calibrated using groundwater and geophysical observations. A good agreement of model simulations with tide-induced head fluctuations, geophysically derived pore water salinities, and measured apparent resistivities was obtained when dykes' hydraulic conductivity, storativity, and effective porosity are respectively about 3, 1, and 1 orders of magnitude lower than the host aquifer. The presence of the dykes results in barrier-like alterations of groundwater flow and saltwater intrusion. Preferential flow paths occur parallel to observed dyke orientations. Freshwater inflows from upland recharge areas concentrate on the land-facing side of the dykes and saltwater penetration is higher on their sea-facing side. This has major implications for managing groundwater resources in dyke-intruded aquifers, including in coastal and island regions and provides wider insights on preferential pathways of groundwater flow and transport in highly heterogeneous aquifer systems.
A noninvasive approach to quantitative measurement of flow through CSF shunts. Technical note.
Stein, S C; Apfel, S
1981-04-01
A method of measuring flow rate through cerebrospinal fluid (CSF) shunts is reported. It consists of two thermistors in series applied to the skin over the shunt tubing. The thermistors respond by a drop in measured temperature following application of an ice cube placed on the skin overlying the proximal shunt tube. The time required for the thermal response to travel between the two thermistors is related to the velocity of flow through the shunt tubing. Flow rate can then be calculated using the internal diameter of the tubing. A series of animal experiments employing a constant infusion of mock CSF through subcutaneously implanted shunt tubing showed excellent correlation between calculated flow rates and actual infusion rates. The device is noninvasive and easily adapted to use in patients. The measurements are readily repeatable.
Computational approach to estimating the effects of blood properties on changes in intra-stent flow.
Benard, Nicolas; Perrault, Robert; Coisne, Damien
2006-08-01
In this study various blood rheological assumptions are numerically investigated for the hemodynamic properties of intra-stent flow. Non-newtonian blood properties have never been implemented in blood coronary stented flow investigation, although its effects appear essential for a correct estimation and distribution of wall shear stress (WSS) exerted by the fluid on the internal vessel surface. Our numerical model is based on a full 3D stent mesh. Rigid wall and stationary inflow conditions are applied. Newtonian behavior, non-newtonian model based on Carreau-Yasuda relation and a characteristic newtonian value defined with flow representative parameters are introduced in this research. Non-newtonian flow generates an alteration of near wall viscosity norms compared to newtonian. Maximal WSS values are located in the center part of stent pattern structure and minimal values are focused on the proximal stent wire surface. A flow rate increase emphasizes fluid perturbations, and generates a WSS rise except for interstrut area. Nevertheless, a local quantitative analysis discloses an underestimation of WSS for modelisation using a newtonian blood flow, with clinical consequence of overestimate restenosis risk area. Characteristic viscosity introduction appears to present a useful option compared to rheological modelisation based on experimental data, with computer time gain and relevant results for quantitative and qualitative WSS determination.
Flow visualization and numerical analysis of a coflowing jet - A three-dimensional approach
NASA Technical Reports Server (NTRS)
Agui, Juan C.; Hesselink, Lambertus
1988-01-01
The instabilities of an acoustically excited coflowing jet are investigated by using a time series of cross-sections of large-scale structures present in the flow and by a fully three-dimensional numerical simulation via the vortex-element method. These structures are first revealed by a flow-visualization technique based on smoke seeding the inner jet flow and observing the flow cross-sections as the structures are convected past a stationary sheet of laser light. Usage of image-processing techniques along with computer graphics allows the full three-dimensional reconstruction of the structure. The general morphology of the flow is determined from the reconstructed views and shows that the vorticity is mainly concentrated into a single large-scale vortex ring. Hypotheses regarding the nature and origin of the longitudinal instabilities observed in the flow can be drawn from the reconstructed views, and are supported by the numerical simulations. Quantitative values such as the surface-to-volume ratio and the entrainment level are also obtained from the experimental data. The onset of streamwise vorticity and its distribution are derived from the numerical calculations as well. Three-dimensional views and a holographic display of a characteristic eddy are also presented.
Instability of cooperative adaptive cruise control traffic flow: A macroscopic approach
NASA Astrophysics Data System (ADS)
Ngoduy, D.
2013-10-01
This paper proposes a macroscopic model to describe the operations of cooperative adaptive cruise control (CACC) traffic flow, which is an extension of adaptive cruise control (ACC) traffic flow. In CACC traffic flow a vehicle can exchange information with many preceding vehicles through wireless communication. Due to such communication the CACC vehicle can follow its leader at a closer distance than the ACC vehicle. The stability diagrams are constructed from the developed model based on the linear and nonlinear stability method for a certain model parameter set. It is found analytically that CACC vehicles enhance the stabilization of traffic flow with respect to both small and large perturbations compared to ACC vehicles. Numerical simulation is carried out to support our analytical findings. Based on the nonlinear stability analysis, we will show analytically and numerically that the CACC system better improves the dynamic equilibrium capacity over the ACC system. We have argued that in parallel to microscopic models for CACC traffic flow, the newly developed macroscopic will provide a complete insight into the dynamics of intelligent traffic flow.
NASA Astrophysics Data System (ADS)
Liu, Zhongqiu; Sun, Zhenbang; Li, Baokuan
2017-04-01
Lagrangian tracking model combined with Eulerian multi-phase model is employed to predict the time-dependent argon-steel-slag-air quasi-four-phase flow inside a slab continuous casting mold. The Eulerian approach is used for the description of three phases (molten steel, liquid slag, and air at the top of liquid slag layer). The dispersed argon bubble injected from the SEN is treated in the Lagrangian way. The complex interfacial momentum transfers between various phases are considered. Validation is supported by the measurement data of cold model experiments and industrial practice. Close agreements were achieved for the gas volume fraction, liquid flow pattern, level fluctuation, and exposed slag eye phenomena. Many known phenomena and new predictions were successfully reproduced using this model. The vortex slag entrapment phenomenon at the slag-steel interface was obtained using this model, some small slag drops are sucked deep into the liquid pool of molten steel. Varying gas flow rates have a large effect on the steel flow pattern in the upper recirculation zone. Three typical flow patterns inside the mold with different argon gas flow rates have been obtained: double roll, three roll, and single roll. Effects of argon gas flow rate, casting speed, and slag layer thickness on the exposed slag eye and level fluctuation at the slag-steel interface were studied. A dimensionless value of H ave/ h was proposed to describe the time-averaged level fluctuation of slag-steel interface. The exposed slag eye near the SEN would be formed when the value of H ave/ h is larger than 0.4.
NASA Astrophysics Data System (ADS)
Liu, Zhongqiu; Sun, Zhenbang; Li, Baokuan
2016-12-01
Lagrangian tracking model combined with Eulerian multi-phase model is employed to predict the time-dependent argon-steel-slag-air quasi-four-phase flow inside a slab continuous casting mold. The Eulerian approach is used for the description of three phases (molten steel, liquid slag, and air at the top of liquid slag layer). The dispersed argon bubble injected from the SEN is treated in the Lagrangian way. The complex interfacial momentum transfers between various phases are considered. Validation is supported by the measurement data of cold model experiments and industrial practice. Close agreements were achieved for the gas volume fraction, liquid flow pattern, level fluctuation, and exposed slag eye phenomena. Many known phenomena and new predictions were successfully reproduced using this model. The vortex slag entrapment phenomenon at the slag-steel interface was obtained using this model, some small slag drops are sucked deep into the liquid pool of molten steel. Varying gas flow rates have a large effect on the steel flow pattern in the upper recirculation zone. Three typical flow patterns inside the mold with different argon gas flow rates have been obtained: double roll, three roll, and single roll. Effects of argon gas flow rate, casting speed, and slag layer thickness on the exposed slag eye and level fluctuation at the slag-steel interface were studied. A dimensionless value of H ave/h was proposed to describe the time-averaged level fluctuation of slag-steel interface. The exposed slag eye near the SEN would be formed when the value of H ave/h is larger than 0.4.
NASA Astrophysics Data System (ADS)
Dalzell, B. J.; Gassman, P. W.; Kling, C.
2015-12-01
In the Minnesota River Basin, sediments originating from failing stream banks and bluffs account for the majority of the riverine load and contribute to water quality impairments in the Minnesota River as well as portions of the Mississippi River upstream of Lake Pepin. One approach for mitigating this problem may be targeted wetland restoration in Minnesota River Basin tributaries in order to reduce the magnitude and duration of peak flow events which contribute to bluff and stream bank failures. In order to determine effective arrangements and properties of wetlands to achieve peak flow reduction, we are employing a genetic algorithm approach coupled with a SWAT model of the Cottonwood River, a tributary of the Minnesota River. The genetic algorithm approach will evaluate combinations of basic wetland features as represented by SWAT: surface area, volume, contributing area, and hydraulic conductivity of the wetland bottom. These wetland parameters will be weighed against economic considerations associated with land use trade-offs in this agriculturally productive landscape. Preliminary results show that the SWAT model is capable of simulating daily hydrology very well and genetic algorithm evaluation of wetland scenarios is ongoing. Anticipated results will include (1) combinations of wetland parameters that are most effective for reducing peak flows, and (2) evaluation of economic trade-offs between wetland restoration, water quality, and agricultural productivity in the Cottonwood River watershed.
NASA Astrophysics Data System (ADS)
Calder, E. S.; Pitman, B.; Wolpert, R.; Bayarri, S.; Spiller, E.; Berger, J.
2009-05-01
It is increasingly being understood that development of mathematical models of a geophysical phenomena, while a fundamental step, is only part of the process of modeling and predicting inundation limits for natural hazards. In this work we combine data from hundreds of observed pyroclastic flows at the Soufriere Hills Volcano, Montserrat, a geophysical flow model, and statistical modeling to derive a new methodology for generating probabilistic hazard maps. The initial step consists of estimating probabilities of inundation at particular discrete points of interest (e.g. airport and Plymouth). The methodology starts with a computer model of the geophysical process, in this case the TITAN2D model that has been developed for modeling geophysical mass flows. A key input to the computer model is the probability distribution for the initial volume and direction of the flows based on observed data. An important limitation is that for modeling purposes, the observations represent relatively scarce datasets, while from a volcanological perspective datasets such as those from the prolonged and relatively well-monitored eruption of the Soufriere Hills Volcano, are as complete as can be realistically obtained. By combining flow event data, probability modeling and statistical methods, a probability distribution of severity and frequency of flow events is derived. Understanding and predicting the effects of volcanic hazards involves understanding the extreme event tail (the largest flow events) but this is notoriously difficult, especially with the limited data and prohibitively expensive to compute.. Instead a statistical emulator (or surrogate of the computer model) is used, a computationally cheap response surface approximating the output of the flow simulations, which is constructed based on carefully chosen computer model runs. The speed of the emulator then allows to 'solve the inverse problem': that is, to determine regions of inputs values (characteristics of the flow
NASA Astrophysics Data System (ADS)
Priede, J.; Gerbeth, G.
2005-11-01
A theoretical study is presented of the effect of a radially converging melt flow, which is directed away from the solidification front, on the radial solute segregation in simple solidification models. We show that the classical Burton-Prim-Slichter (BPS) solution describing the effect of a diverging flow on the solute incorporation into the solidifying material breaks down for the flows converging along the solidification front. The breakdown is caused by a divergence of the integral defining the effective boundary layer thickness which is the basic concept of the BPS theory. Although such a divergence can formally be avoided by restricting the axial extension of the melt to a layer of finite height, radially uniform solute distributions are possible only for weak melt flows with an axial velocity away from the solidification front comparable to the growth rate. There is a critical melt velocity for each growth rate at which the solution passes through a singularity and becomes physically inconsistent for stronger melt flows. To resolve these inconsistencies we consider a solidification front presented by a disk of finite radius R0 subject to a strong converging melt flow and obtain an analytic solution showing that the radial solute concentration depends on the radius r as ˜ln(R0/r) and ˜ln(R0/r) close to the rim and at large distances from it. The logarithmic increase of concentration is limited in the vicinity of the symmetry axis by the diffusion becoming effective at a distance comparable to the characteristic thickness of the solute boundary layer. The converging flow causes a solute pile-up forming a logarithmic concentration peak at the symmetry axis which might be an undesirable feature for crystal growth processes.
NASA Astrophysics Data System (ADS)
Breugem, W. P.; Boersma, B. J.
2005-02-01
A direct numerical simulation (DNS) has been performed of turbulent channel flow over a three-dimensional Cartesian grid of 30×20×9 cubes in, respectively, the streamwise, spanwise, and wall-normal direction. The grid of cubes mimics a permeable wall with a porosity of 0.875. The flow field is resolved with 600×400×400 mesh points. To enforce the no-slip and no-penetration conditions on the cubes, an immersed boundary method is used. The results of the DNS are compared with a second DNS in which a continuum approach is used to model the flow through the grid of cubes. The continuum approach is based on the volume-averaged Navier-Stokes (VANS) equations [S. Whitaker, "The Forchheimer equation: a theoretical development," Transp. Porous Media 25, 27 (1996)] for the volume-averaged flow field. This method has the advantage that it requires less computational power than the direct simulation of the flow through the grid of cubes. More in general, for complex porous media one is usually forced to use the VANS equations, because a direct simulation would not be possible with present-day computer facilities. A disadvantage of the continuum approach is that in order to solve the VANS equations, closures are needed for the drag force and the subfilter-scale stress. For porous media, the latter can often be neglected. In the present work, a relation for the drag force is adopted based on the Irmay ["Modèles théoriques d'écoulement dans les corps poreux," Bulletin Rilem 29, 37 (1965)] and the Burke-Plummer model [R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena (Wiley, New York, 2002)], with the model coefficients determined from simulations reported by W. P. Breugem, B. J. Boersma, and R. E. Uittenbogaard ["Direct numerical simulation of plane channel flow over a 3D Cartesian grid of cubes," Proceedings of the Second International Conference on Applications of Porous Media, edited by A. H. Reis and A. F. Miguel (Évora Geophysics Center,
Gülan, Utku; Binter, Christian; Kozerke, Sebastian; Holzner, Markus
2017-03-12
Today, the functional and risk assessment of stenosed arteries is mostly based on ultrasound Doppler blood flow velocity measurements or catheter pressure measurements, which rely on several assumptions. Alternatively, blood velocity including turbulent kinetic energy (TKE) may be measured using MRI. The aim of the present study is to validate a TKE-based approach that relies on the fact that turbulence production is dominated by the flow's shear to determine the total irreversible energy loss from MRI scans. Three-dimensional particle tracking velocimetry (3D-PTV) and phase-contrast magnetic resonance imaging (PC-MRI) simulations were performed in an anatomically accurate, compliant, silicon aortic phantom. We found that measuring only the laminar viscous losses does not reflect the true losses of stenotic flows since the contribution of the turbulent losses to the total loss become more dominant for more severe stenosis types (for example, the laminar loss is 0.0094±0.0015W and the turbulent loss is 0.0361±0.0015W for the Remax=13,800 case, where Remax is the Reynolds number based on the velocity in the vena-contracta). We show that the commonly used simplified and modified Bernoulli's approaches overestimate the total loss, while the new TKE-based method proposed here, referred to as "shear scaling" approach, results in a good agreement between 3D-PTV and simulated PC-MRI (mean error is around 10%). In addition, we validated the shear scaling approach on a geometry with post-stenotic dilatation using numerical data by Casas et al. (2016). The shear scaling-based method may hence be an interesting alternative for irreversible energy loss estimation to replace traditional approaches for clinical use. We expect that our results will evoke further research, in particular patient studies for clinical implementation of the new method.
NASA Astrophysics Data System (ADS)
Jomelli, Vincent; Pavlova, Irina; Eckert, Nicolas; Grancher, Delphine; Brunstein, Daniel
2015-12-01
How can debris flow occurrences be modelled at regional scale and take both environmental and climatic conditions into account? And, of the two, which has the most influence on debris flow activity? In this paper, we try to answer these questions with an innovative Bayesian hierarchical probabilistic model that simultaneously accounts for how debris flows respond to environmental and climatic variables. In it, full decomposition of space and time effects in occurrence probabilities is assumed, revealing an environmental and a climatic trend shared by all years/catchments, respectively, clearly distinguished from residual "random" effects. The resulting regional and annual occurrence probabilities evaluated as functions of the covariates make it possible to weight the respective contribution of the different terms and, more generally, to check the model performances at different spatio-temporal scales. After suitable validation, the model can be used to make predictions at undocumented sites and could be used in further studies for predictions under future climate conditions. Also, the Bayesian paradigm easily copes with missing data, thus making it possible to account for events that may have been missed during surveys. As a case study, we extract 124 debris flow event triggered between 1970 and 2005 in 27 catchments located in the French Alps from the French national natural hazard survey and model their variability of occurrence considering environmental and climatic predictors at the same time. We document the environmental characteristics of each debris flow catchment (morphometry, lithology, land cover, and the presence of permafrost). We also compute 15 climate variables including mean temperature and precipitation between May and October and the number of rainy days with daily cumulative rainfall greater than 10/15/20/25/30/40 mm day- 1. Application of our model shows that the combination of environmental and climatic predictors explained 77% of the overall
Unsteady Hartmann Two-Phase Flow: The Riemann-Sum Approximation Approach
NASA Astrophysics Data System (ADS)
Jha, B. K.; Babila, C. T.; Isa, S.
2016-12-01
We consider the time dependent Hartmann flow of a conducting fluid in a channel formed by two horizontal parallel plates of infinite extent, there being a layer of a non-conducting fluid between the conducting fluid and the upper channel wall. The flow formation of conducting and non-conducting fluids is coupled by equating the velocity and shear stress at the interface. The unsteady flow formation inside the channel is caused by a sudden change in the pressure gradient. The relevant partial differential equations capturing the present physical situation are transformed into ordinary differential equations using the Laplace transform technique. The ordinary differential equations are then solved analytically and the Riemann-sum approximation method is used to invert the Laplace domain into time domain. The solution obtained is validated by comparisons with the closed form solutions obtained for steady states which have been derived separately and also by the implicit finite difference method. The variation of velocity, mass flow rate and skin-friction on both plates for various physical parameters involved in the problem are reported and discussed with the help of line graphs. It was found that the effect of changes of the electric load parameter is to aid or oppose the flow as compared to the short-circuited case.
Kinetics-based phase change approach for VOF method applied to boiling flow
NASA Astrophysics Data System (ADS)
Cifani, Paolo; Geurts, Bernard; Kuerten, Hans
2014-11-01
Direct numerical simulations of boiling flows are performed to better understand the interaction of boiling phenomena with turbulence. The multiphase flow is simulated by solving a single set of equations for the whole flow field according to the one-fluid formulation, using a VOF interface capturing method. Interface terms, related to surface tension, interphase mass transfer and latent heat, are added at the phase boundary. The mass transfer rate across the interface is derived from kinetic theory and subsequently coupled with the continuum representation of the flow field. The numerical model was implemented in OpenFOAM and validated against 3 cases: evaporation of a spherical uniformly heated droplet, growth of a spherical bubble in a superheated liquid and two dimensional film boiling. The computational model will be used to investigate the change in turbulence intensity in a fully developed channel flow due to interaction with boiling heat and mass transfer. In particular, we will focus on the influence of the vapor bubble volume fraction on enhancing heat and mass transfer. Furthermore, we will investigate kinetic energy spectra in order to identify the dynamics associated with the wakes of vapor bubbles. Department of Applied Mathematics, 7500 AE Enschede, NL.
NASA Astrophysics Data System (ADS)
Liu, Zhongqiu; Li, Linmin; Qi, Fengsheng; Li, Baokuan; Jiang, Maofa; Tsukihashi, Fumitaka
2015-02-01
A population balance model based on the multiple-size-group (MUSIG) approach has been developed to investigate the polydispersed bubbly flow inside the slab continuous-casting mold and bubble behavior including volume fraction, breakup, coalescence, and size distribution. The Eulerian-Eulerian approach is used to describe the equations of motion of the two-phase flow. All the non-drag forces (lift force, virtual mass force, wall lubrication force, and turbulent dispersion force) and drag force are incorporated in this model. Sato and Sekiguchi model is used to account for the bubble-induced turbulence. Luo and Svendsen model and Prince and Blanch model are used to describe the bubbles breakup and coalescence behavior, respectively. A 1/4th water model of the slab continuous-casting mold was applied to investigate the distribution and size of bubbles by injecting air through a circumferential inlet chamber which was made of the specially-coated samples of mullite porous brick, which is used for the actual upper nozzle. Against experimental data, numerical results showed good agreement for the gas volume fraction and local bubble Sauter mean diameter. The bubble Sauter mean diameter in the upper recirculation zone decreases with increasing water flow rate and increases with increasing gas flow rate. The distribution of bubble Sauter mean diameter along the width direction of the upper mold increases first, and then gradually decreases from the SEN to the narrow wall. Close agreements between the predictions and measurements demonstrate the capability of the MUSIG model in modeling bubbly flow inside the continuous-casting mold.
An approach to the constrained design of natural laminar flow airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford Earl
1995-01-01
A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integml turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the larninar flow toward the desired amounl An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.
Flow Visualization at Cryogenic Conditions Using a Modified Pressure Sensitive Paint Approach
NASA Technical Reports Server (NTRS)
Watkins, A. Neal; Goad, William K.; Obara, Clifford J.; Sprinkle, Danny R.; Campbell, Richard L.; Carter, Melissa B.; Pendergraft, Odis C., Jr.; Bell, James H.; Ingram, JoAnne L.; Oglesby, Donald M.
2005-01-01
A modification to the Pressure Sensitive Paint (PSP) method was used to visualize streamlines on a Blended Wing Body (BWB) model at full-scale flight Reynolds numbers. In order to achieve these conditions, the tests were carried out in the National Transonic Facility operating under cryogenic conditions in a nitrogen environment. Oxygen is required for conventional PSP measurements, and several tests have been successfully completed in nitrogen environments by injecting small amounts (typically < 3000 ppm) of oxygen into the flow. A similar technique was employed here, except that air was purged through pressure tap orifices already existent on the model surface, resulting in changes in the PSP wherever oxygen was present. The results agree quite well with predicted results obtained through computational fluid dynamics analysis (CFD), which show this to be a viable technique for visualizing flows without resorting to more invasive procedures such as oil flow or minitufts.
Flow rate estimation by optical coherence tomography using contrast dilution approach
NASA Astrophysics Data System (ADS)
Štohanzlová, Petra; Kolář, Radim
2015-07-01
This paper describes experiments and methodology for flow rate estimation using optical coherence tomography and dilution method in single fiber setup. The single fiber is created from custom made glass capillary and polypropylene hollow fiber. As a data source, measurements on single fiber phantom with continuous flow of carrier medium and bolus of Intralipid solution as a contrast agent were used using Thorlabs OCT OCS1300SS. The measured data were processed by methods of image processing, in order to precisely align the individual images in the sequence and extract dilution curves from the area inside the fiber. An experiment proved that optical coherence tomography can be used for flow rate estimation by the dilution method with precision around 7%.
An Approach to the Constrained Design of Natural Laminar Flow Airfoils
NASA Technical Reports Server (NTRS)
Green, Bradford E.
1997-01-01
A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integral turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the laminar flow toward the desired amount. An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.
Huang, Qiu; Peng, Qiyu; Huang, Bin; Cheryauka, Arvi; Gullberg, Grant T.
2008-05-15
The measurement of flow obtained using continuous wave Doppler ultrasound is formulated as a directional projection of a flow vector field. When a continuous ultrasound wave bounces against a flowing particle, a signal is backscattered. This signal obtains a Doppler frequency shift proportional to the speed of the particle along the ultrasound beam. This occurs for each particle along the beam, giving rise to a Doppler velocity spectrum. The first moment of the spectrum provides the directional projection of the flow along theultrasound beam. Signals reflected from points further away from the detector will have lower amplitude than signals reflected from points closer to the detector. The effect is very much akin to that modeled by the attenuated Radon transform in emission computed tomography.A least-squares method was adopted to reconstruct a 2D vector field from directional projection measurements. Attenuated projections of only the longitudinal projections of the vector field were simulated. The components of the vector field were reconstructed using the gradient algorithm to minimize a least-squares criterion. This result was compared with the reconstruction of longitudinal projections of the vector field without attenuation. Ifattenuation is known, the algorithm was able to accurately reconstruct both components of the full vector field from only one set of directional projection measurements. A better reconstruction was obtained with attenuation than without attenuation implying that attenuation provides important information for the reconstruction of flow vector fields.This confirms previous work where we showed that knowledge of the attenuation distribution helps in the reconstruction of MRI diffusion tensor fields from fewer than the required measurements. In the application of ultrasound the attenuation distribution is obtained with pulse wave transmission computed tomography and flow information is obtained with continuous wave Doppler.
An Approach to Adaptive Correction Factors in Depth-Averaged Model for Debris Flows
NASA Astrophysics Data System (ADS)
Tai, Yih-Chin; Cheng, Chin-Kai; Lai, Guan-Cen
2016-04-01
In modeling the debris flows, the governing equations are often given in depth-averaged form, where scaling analysis is employed to reduce the complexity and expense in computation. As a result, the non-uniform distributions of the sediment concentration and velocity along the flow thickness bring the correction parameters into the equation system. Since the flows are generally not at steady state, these distributions vary dynamically, so that the values of the correction factors should not be given by constant values. With the concept of two-phase mixture, we revisit the depth-averaged balance equations, where four correction factors are present and inevitable in the resultant model equations if the distributions of the sediment concentration and velocity along the flow thickness are non-uniform. Through theoretical analysis and experimental investigation, we found that a piecewise-linear distribution for velocity and a linear distribution of sediment concentration in the immature debris flows (where the clear water exists) seem plausible. This assumption may significantly simplify the complicated determination of the correction factors. In the resultant model equations, the correcting parameters due to the non-uniform distributions are present, which are of significant impacts on the characteristic of the equation system, and play crucial roles in performing the numerical simulation. In this study, the values of these factors with respect to the corresponding profiles are investigated. By means of numerical examples, we shall illustrate their impacts on the flow behaviors, such as the concentration variation, the geometry of the deposit and the maximum run-out distance.
NASA Astrophysics Data System (ADS)
Liu, X.
2013-12-01
In many natural and human-impacted rivers, the porous sediment beds are either fully or partially covered by large roughness elements, such as gravels and boulders. The existence of these large roughness elements, which are in direct contact with the turbulent river flow, changes the dynamics of mass and momentum transfer across the river bed. It also impacts the overall hydraulics in the river channel and over time, indirectly influences the geomorphological evolution of the system. Ideally, one should resolve each of these large roughness elements in a computational fluid model. This approach is apparently not feasible due to the prohibitive computational cost. Considering a typical river bed with armoring, the distribution of sediment sizes usually shows significant vertical variations. Computationally, it poses great challenge to resolve all the size scales. Similar multiscale problem exists in the much broader porous media flow field. To cope with this, we propose a hybrid computational approach where the large surface roughness elements are resolved using immersed boundary method and sediment layers below (usually finer) are modeled by adding extra drag terms in momentum equations. Large roughness elements are digitized using a 3D laser scanner. They are put into the computational domain using the collision detection and rigid body dynamics algorithms which guarantees realistic and physically-correct spatial arrangement of the surface elements. Simulation examples have shown the effectiveness of the hybrid approach which captures the effect of the surface roughness on the turbulent flow as well as the hyporheic flow pattern in and out of the bed.
NASA Astrophysics Data System (ADS)
Bonelli, Francesco; Tuttafesta, Michele; Colonna, Gianpiero; Cutrone, Luigi; Pascazio, Giuseppe
2017-10-01
This paper describes the most advanced results obtained in the context of fluid dynamic simulations of high-enthalpy flows using detailed state-to-state air kinetics. Thermochemical non-equilibrium, typical of supersonic and hypersonic flows, was modeled by using both the accurate state-to-state approach and the multi-temperature model proposed by Park. The accuracy of the two thermochemical non-equilibrium models was assessed by comparing the results with experimental findings, showing better predictions provided by the state-to-state approach. To overcome the huge computational cost of the state-to-state model, a multiple-nodes GPU implementation, based on an MPI-CUDA approach, was employed and a comprehensive code performance analysis is presented. Both the pure MPI-CPU and the MPI-CUDA implementations exhibit excellent scalability performance. GPUs outperform CPUs computing especially when the state-to-state approach is employed, showing speed-ups, of the single GPU with respect to the single-core CPU, larger than 100 in both the case of one MPI process and multiple MPI process.
NASA Astrophysics Data System (ADS)
Huang, Rong-Hwa; Yang, Chang-Lin; Hsu, Chun-Ting
2015-12-01
Flow shop production system - compared to other economically important production systems - is popular in real manufacturing environments. This study focuses on the flow shop with multiprocessor scheduling problem (FSMP), and develops an improved particle swarm optimisation heuristic to solve it. Additionally, this study designs an integer programming model to perform effectiveness and robustness testing on the proposed heuristic. Experimental results demonstrate a 10% to 50% improvement in the effectiveness of the proposed heuristic in small-scale problem tests, and a 10% to 40% improvement in the robustness of the heuristic in large-scale problem tests, indicating extremely satisfactory performance.
A bottom-up approach to estimate dry weather flow in minor sewer networks.
Elías-Maxil, J A; van der Hoek, Jan Peter; Hofman, Jan; Rietveld, Luuk
2014-01-01
In order to evaluate the feasibility of installing decentralised installations for wastewater reuse in cities, information about flows at specific spots of a sewer is needed. However, measuring intermittent flows in partially filled conduits is a technical task which is sometimes difficult to accomplish. This paper describes a method to model intermittent discharges in small sewers by linking a stochastic model for wastewater discharge to a hydraulic model to predict the attenuation of the discharges and its impact on the arrival time to a defined spot. The method was validated in a case study. The model estimated adequately the wastewater discharges on working days.
van Bussel, Frank C G; van Bussel, Bas C T; Hoeks, Arnold P G; Op 't Roodt, Jos; Henry, Ronald M A; Ferreira, Isabel; Vanmolkot, Floris H M; Schalkwijk, Casper G; Stehouwer, Coen D A; Reesink, Koen D
2015-01-01
Flow-mediated dilation is aimed at normalization of local wall shear stress under varying blood flow conditions. Blood flow velocity and vessel diameter are continuous and opposing influences that modulate wall shear stress. We derived an index FMDv to quantify wall shear stress normalization performance by flow-mediated dilation in the brachial artery. In 22 fasting presumed healthy men, we first assessed intra- and inter-session reproducibilities of two indices pFMDv and mFMDv, which consider the relative peak and relative mean hyperemic change in flow velocity, respectively. Second, utilizing oral glucose loading, we evaluated the tracking performance of both FMDv indices, in comparison with existing indices [i.e., the relative peak diameter increase (%FMD), the peak to baseline diameter ratio (Dpeak/Dbase), and the relative peak diameter increase normalized to the full area under the curve of blood flow velocity with hyperemia (FMD/shearAUC) or with area integrated to peak hyperemia (FMD/shearAUC_peak)]. Inter-session and intra-session reproducibilities for pFMDv, mFMDv and %FMD were comparable (intra-class correlation coefficients within 0.521-0.677 range). Both pFMDv and mFMDv showed more clearly a reduction after glucose loading (reduction of ~45%, p≤0.001) than the other indices (% given are relative reductions): %FMD (~11%, p≥0.074); Dpeak/Dbase (~11%, p≥0.074); FMD/shearAUC_peak (~20%, p≥0.016) and FMD/shearAUC (~38%, p≤0.038). Further analysis indicated that wall shear stress normalization under normal (fasting) conditions is already far from ideal (FMDv < 1), which (therefore) does not materially change with glucose loading. Our approach might be useful in intervention studies to detect intrinsic changes in shear stress normalization performance in conduit arteries.
A MULTIPLE GRID APPROACH FOR OPEN CHANNEL FLOWS WITH STRONG SHOCKS. (R825200)
Explicit finite difference schemes are being widely used for modeling open channel flows accompanied with shocks. A characteristic feature of explicit schemes is the small time step, which is limited by the CFL stability condition. To overcome this limitation,...
Innovative Approaches for Urban Watershed Management Wet-Weather Flow Management and Control
The overall objective of this project was to identify innovative strategies for managing the effects of wet-weather flow (WWF) control and failing infrastructure in an urban setting. The intent was to establish areas where external information can benefit US Environmental Protec...
Innovative Approaches for Urban Watershed Management Wet-Weather Flow Management and Control
The overall objective of this project was to identify innovative strategies for managing the effects of wet-weather flow (WWF) control and failing infrastructure in an urban setting. The intent was to establish areas where external information can benefit US Environmental Protec...
URBAN WET-WEATHER FLOW MICROBIAL CONTAMINATION: HIGH-RATE TREATMENT APPROACHES
fThis presentation is on high-rate disinfection of wet-weather flow (WWF) and pretreatment processes of suspended solids to enhance the disinfection. A discussion of pretreatment processes and of the newest disinfection technologies used for WWF is included, along with the feasib...
A MULTIPLE GRID APPROACH FOR OPEN CHANNEL FLOWS WITH STRONG SHOCKS. (R825200)
Explicit finite difference schemes are being widely used for modeling open channel flows accompanied with shocks. A characteristic feature of explicit schemes is the small time step, which is limited by the CFL stability condition. To overcome this limitation,...
Novel flow cytometry approach to identify bronchial epithelial cells from healthy human airways
Maestre-Batlle, Danay; Pena, Olga M.; Hirota, Jeremy A.; Gunawan, Evelyn; Rider, Christopher F.; Sutherland, Darren; Alexis, Neil E.; Carlsten, Chris
2017-01-01
Sampling various compartments within the lower airways to examine human bronchial epithelial cells (HBEC) is essential for understanding numerous lung diseases. Conventional methods to identify HBEC in bronchoalveolar lavage (BAL) and wash (BW) have throughput limitations in terms of efficiency and ensuring adequate cell numbers for quantification. Flow cytometry can provide high-throughput quantification of cell number and function in BAL and BW samples, while requiring low cell numbers. To date, a flow cytometric method to identify HBEC recovered from lower human airway samples is unavailable. In this study we present a flow cytometric method identifying HBEC as CD45 negative, EpCAM/pan-cytokeratin (pan-CK) double-positive population after excluding debris, doublets and dead cells from the analysis. For validation, the HBEC panel was applied to primary HBEC resulting in 98.6% of live cells. In healthy volunteers, HBEC recovered from BAL (2.3% of live cells), BW (32.5%) and bronchial brushing samples (88.9%) correlated significantly (p = 0.0001) with the manual microscopy counts with an overall Pearson correlation of 0.96 across the three sample types. We therefore have developed, validated, and applied a flow cytometric method that will be useful to interrogate the role of the respiratory epithelium in multiple lung diseases. PMID:28165060
Pipe Flow Simulation Software: A Team Approach to Solve an Engineering Education Problem.
ERIC Educational Resources Information Center
Engel, Renata S.; And Others
1996-01-01
A computer simulation program for use in the study of fluid mechanics is described. The package is an interactive tool to explore the fluid flow characteristics of a pipe system by manipulating the physical construction of the system. The motivation, software design requirements, and specific details on how its objectives were met are presented.…
Shen, Zhiyuan; Feng, Naizhang; Shen, Yi; Lee, Chin-Hui
2013-06-01
In color flow imaging, it is a challenging work to accurately extract blood flow information from ultrasound Doppler echoes dominated by the strong clutter components. In this paper, we provide an in-depth analysis of ridge ensemble empirical mode decomposition (R-EEMD) and compare it with the conventional empirical mode decomposition (EMD) framework. R-EEMD facilitates nonuniform and trial-dependent weights obtained by an optimization procedure during ensemble combination and results in less decomposition errors when compared with the conventional ensemble empirical mode decomposition techniques. A theoretic result is then extended to demonstrate that R-EEMD has an ability to solve the mode mixing problem frequently encountered in EMD and improve the decomposition performance with adequate noise strength when separating a composite two-tone signal. Based on the proposed R-EEMD framework, a novel clutter rejection filter for ultrasound color flow imaging is designed. In a series of simulations, the R-EEMD-based filter achieves a significant improvement on blood flow velocity estimation over the state-of-the-art regression filters and decomposition-based filters, such as eigen-based and EMD filters. An experiment on human carotid artery data also verifies that the R-EEMD algorithm achieves minimum clutter energy and maximum blood-to-clutter energy ratio among all the tested techniques.
Pipe Flow Simulation Software: A Team Approach to Solve an Engineering Education Problem.
ERIC Educational Resources Information Center
Engel, Renata S.; And Others
1996-01-01
A computer simulation program for use in the study of fluid mechanics is described. The package is an interactive tool to explore the fluid flow characteristics of a pipe system by manipulating the physical construction of the system. The motivation, software design requirements, and specific details on how its objectives were met are presented.…
Chakravarty, S; Sen, S
2008-01-01
This theoretical investigation deals with an analysis of pulsatile blood flow in a model bifurcated artery having a stenosis in the parent arterial lumen. The geometry of the bifurcated arterial segment with an implanted stenosis in the parent duct is given an appropriate mathematical shape with the introduction of suitable curvature at the lateral junction and the flow divider. The vascular wall deformability is duly accounted for although the development of atherosclerosis in the arteries reduces its elastic property to some extent. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamic analysis applies two-dimensional unsteady incompressible nonlinear Navier-Stokes equations rewritten in the vorticity-stream function formulation. Following a radial coordinate transformation, these equations are solved numerically by a finite difference scheme with the approximate choice of the inlet and boundary conditions in concert with the biophysical point of view. The final numerical results are highlighted at the end of the paper through the exhibition of the wall shear stress and several time-variant patterns of streamlines and vorticity contours of the flow phenomena, which are highly influenced by the severity of the stenosis and the angle of bifurcation. The applicability of the present model is thus established.
Analysis of Different Approaches to Modeling of the Nozzle Flows in the Near Continuum Regime
2007-12-21
the Near Continuum Regime (Postprint) 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) E.V. Titov & D.A. Levin (Pennsylvania State...of Nozzle Flows in the Near Continuum Regime E.V. Titov ∗ and D.A. Levin† Pennsylvania State University, University Park, PA 16802 N.E. Gimelshein‡ and
NASA Astrophysics Data System (ADS)
Rodrigues, C. Veiga; Palma, J. M. L. M.; Rodrigues, Á. H.
2016-05-01
The atmospheric flow over a mountainous region has been simulated using a model-chain approach, whereby the flow in a larger region was simulated using a mesoscale model with three nesting levels, down to a 3-km horizontal resolution, within which a fourth nesting level was set with a microscale flow solver and a domain with varying horizontal resolution, around 300 m at the site of interest. Two periods in the summer (July) and autumn (November-December) 2005, each with a duration of two weeks, were selected to test the present approach. Two sites were chosen, comprising a total of seven meteorological masts with wind vanes and anemometers at two heights. The microscale solver improved the wind-speed prediction of the mesoscale model in 10 of the 14 anemometers and replicated the high wind speeds, which were under-predicted in the mesoscale model. The wind conditions in summer varied with the daily cycle, related to regional-scale sea breezes and their interaction with local circulations induced by the topography. Regarding the turbulence intensity, the predicted decay with wind-speed increase was in agreement with the measurements. This study shows the need of both models: the microscale model captures the details of the boundary-layer physics, which would not be possible without the boundary conditions provided by the mesoscale model.
NASA Astrophysics Data System (ADS)
Capaccioni, Bruno; Nappi, Giovanni; Valentini, Laura
2001-07-01
Computer-assisted image analysis data of rock fabrics from two quaternary ignimbrites in the Vulsini and Cimini Volcanic Districts of Central Italy are interpreted in terms of transport and depositional mechanisms. Samples were collected vertically at m spaces up two sections through each deposit. The Orvieto-Bagnoregio ignimbrite (OBI) is a non-welded ignimbrite that shows both fluctuations in the mean particle orientation values of up to approximately ±60°, and large variations in the strength of particle iso-orientation with height. The circular frequency distributions of particle orientations are almost always anisotropic and unimodal, in line with a theoretical Von Mises distribution (the circular equivalent of a unimodal, log-normal distribution). In contrast, the welded Cimina ignimbrite (CI) shows vertical homogeneities in mean orientation values with height, and generally lower degrees of anisotropy. Such differences are interpreted as being the results of different depositional mechanisms: incremental deposition at the base of a density-stratified, partially turbulent flow for the OBI; deposition of a laminar mass flow for the CI. In the former case, during transport particles under solidus temperature are subjected to a frictional regime, particles gliding and dispersive pressures, which finally produce size-inverse grading and variable fabric development, depending on the residence time of particles at the basal shear conditions. In the latter case, elongated particles, supported in a laminar flowing viscous matrix, undergo periodic motions which tend to develop parallel-to-flow iso-orientation. Fabric data in the deposit suggest vertical constancy in the rheological properties of the flow, absence of rheological decoupling and (shearing pervasively during transport) a minor importance of plug horizons.
Buoyant displacement flow of immiscible fluids in inclined ducts: A theoretical approach
NASA Astrophysics Data System (ADS)
Hasnain, A.; Alba, K.
2017-05-01
We study the buoyant displacement flow of two immiscible Newtonian fluids in an inclined duct (two-dimensional channel) theoretically. The fluids may have different viscosities. The displacing fluid is denser than the displaced one, i.e., a density-unstable configuration. For simplicity, the fluids are assumed to behave as neutrally wetting in the vicinity of duct walls. The small diameter-to-length ratio of the duct considered (δ ≪1 ) has been used as the perturbation parameter in developing a lubrication model (negligible inertia). Appropriate Navier-slip conditions have been applied at the walls to overcome contact-line problem singularity. The lubrication model developed has then been numerically solved using a robust total variation diminishing finite difference scheme. Completely different flow patterns have been observed compared to the miscible limit. Fluids immiscibility is found to cause a capillary ridge in the vicinity of the displacing front, which diminishes as the surface tension is increased. For small values of surface tension parameter, the fluids immiscibility is found to decelerate the advancement of interpenetrating heavy and light layers. More efficient displacement (less fingering within the displacing layer) has been observed at small density differences and when the displacing fluid is more viscous than the displaced one. The limit of zero imposed velocity corresponding to the exchange flow has further been considered in the lubrication model. An interesting jump in the interface height occurs close to the vicinity of the gate region due to the immiscibility, which has been similarly reported in other recent computational works. Detailed mathematical notes on the similarity solution of the flow at long times are moreover provided. Investigating the short-time dynamics of the flow reveals the dominance of diffusive surface tension effects over buoyancy.
NASA Astrophysics Data System (ADS)
Benard, N.; Pons-Prats, J.; Periaux, J.; Bugeda, G.; Braud, P.; Bonnet, J. P.; Moreau, E.
2016-02-01
The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated flows. Here, a nonthermal surface plasma discharge (dielectric barrier discharge) is installed at the step corner of a backward-facing step ( U 0 = 15 m/s, Re h = 30,000, Re θ = 1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step (objective function #1) and also to measure the wall pressure fluctuation coefficients (objective function #2). An autonomous multi-variable optimization by genetic algorithm is implemented in an experiment for optimizing simultaneously the voltage amplitude, the burst frequency and the duty cycle of the high-voltage signal producing the surface plasma discharge. The single-objective optimization problems concern alternatively the minimization of the objective function #1 and the maximization of the objective function #2. The present paper demonstrates that when coupled with the plasma actuator and the wall pressure sensors, the genetic algorithm can find the optimum forcing conditions in only a few generations. At the end of the iterative search process, the minimum reattaching position is achieved by forcing the flow at the shear layer mode where a large spreading rate is obtained by increasing the periodicity of the vortex street and by enhancing the vortex pairing process. The objective function #2 is maximized for an actuation at half the shear layer mode. In this specific forcing mode, time-resolved PIV shows that the vortex pairing is reduced and that the strong fluctuations of the wall pressure coefficients result from the periodic passages of flow structures whose size corresponds to the height of the step model.
NASA Astrophysics Data System (ADS)
Meneveau, Charles; Johnson, Perry; Hamilton, Stephen; Burns, Randal
2016-11-01
An intrinsic property of turbulent flows is the exponential deformation of fluid elements along Lagrangian paths. The production of enstrophy by vorticity stretching follows from a similar mechanism in the Lagrangian view, though the alignment statistics differ and viscosity prevents unbounded growth. In this paper, the stretching properties of fluid elements and vorticity along Lagrangian paths are studied in a channel flow at Reτ = 1000 and compared with prior, known results from isotropic turbulence. To track Lagrangian paths in a public database containing Direct Numerical Simulation (DNS) results, the task-parallel approach previously employed in the isotropic database is extended to the case of flow in a bounded domain. It is shown that above 100 viscous units from the wall, stretching statistics are equal to their isotropic values, in support of the local isotropy hypothesis. Normalized by dissipation rate, the stretching in the buffer layer and below is less efficient due to less favorable alignment statistics. The Cramér function characterizing cumulative Lagrangian stretching statistics shows that overall the channel flow has about half of the stretching per unit dissipation compared with isotropic turbulence. Supported by a National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1232825, and by National Science Foundation Grants CBET-1507469, ACI-1261715, OCI-1244820 and by JHU IDIES.
Mager, R; Balzereit, C; Gust, K; Hüsch, T; Herrmann, T; Nagele, U; Haferkamp, A; Schilling, D
2016-05-01
Passive removal of stone fragments in the irrigation stream is one of the characteristics in continuous-flow PCNL instruments. So far the physical principle of this so-called vacuum cleaner effect has not been fully understood yet. The aim of the study was to empirically prove the existence of the vacuum cleaner effect and to develop a physical hypothesis and generate a mathematical model for this phenomenon. In an empiric approach, common low-pressure PCNL instruments and conventional PCNL sheaths were tested using an in vitro model. Flow characteristics were visualized by coloring of irrigation fluid. Influence of irrigation pressure, sheath diameter, sheath design, nephroscope design and position of the nephroscope was assessed. Experiments were digitally recorded for further slow-motion analysis to deduce a physical model. In each tested nephroscope design, we could observe the vacuum cleaner effect. Increase in irrigation pressure and reduction in cross section of sheath sustained the effect. Slow-motion analysis of colored flow revealed a synergism of two effects causing suction and transportation of the stone. For the first time, our model showed a flow reversal in the sheath as an integral part of the origin of the stone transportation during vacuum cleaner effect. The application of Bernoulli's equation provided the explanation of these effects and confirmed our experimental results. We widen the understanding of PCNL with a conclusive physical model, which explains fluid mechanics of the vacuum cleaner effect.
NASA Astrophysics Data System (ADS)
Adesemowo, Morakinyo; Shelton, John
2016-11-01
Previous experimental and numerical investigations involving lid-driven cavity flows with particle suspensions have primarily focused on particle tracking and the visualization of complex three-dimensional structures that compose the flow field. However, these particle suspensions and their resulting particle-particle interactions could also be viewed as a system of time-dependent perturbation equations to the steady-state Navier-Stokes equations and could affect both the stability and steady-state characteristics of the two-dimensional lid-driven cavity system. In this investigation, an Eulerian-Lagrangian approach to modeling particle suspensions in the lid-driven cavity is utilized in FV-CFD simulations to investigate the effect particle density, area fraction, and Reynolds number have on the two-dimensional flow characteristics of a laminar fluid. Observations have indicated that the development of the primary vortex in the lid-driven cavity varies according to the area fraction of particle suspensions in the system; transitioning from development via an adverse pressure gradient at the top-right corner of the cavity towards particle-laden behavior where particle-particle interactions dominate the development of the primary vortex. Dynamic responses were also observed for particle systems of less dense particles. Finally, a comparison between flows perturbed using disturbance velocities and from particle interactions was performed.
A full-Bayesian approach to the inverse problem for steady-state groundwater flow and heat transport
NASA Astrophysics Data System (ADS)
Jiang, Yefang; Woodbury, Allan D.
2006-12-01
The full (hierarchal) Bayesian approach proposed by Woodbury & Ulrych and Jiang et al. is extended to the inverse problem for 2-D steady-state groundwater flow and heat transport. A stochastic conceptual framework for the heat flow and groundwater flow is adopted. A perturbation of both the groundwater flow and the advection-conduction heat transport equations leads to a linear formulation between heads, temperature and logarithm transmissivity [denoted as ln (T)]. A Bayesian updating procedure similar to that of Woodbury & Ulrych can then be performed. This new algorithm is examined against a generic example through simulations. The prior mean, variance and integral scales of ln (T) (hyperparameters) are treated as random variables and their pdfs are determined from maximum entropy considerations. It is also assumed that the statistical properties of the noise in the hydraulic head and temperature measurements are also uncertain. Uncertainties in all pertinent hyperparameters are removed by marginalization. It is found that the use of temperature measurements is showed to further improve the ln (T) estimates for the test case in comparison to the updated ln (T) field conditioned on ln (T) and head data; the addition of temperature data without hydraulic head data to the update also aids refinement of the ln (T) field compared to simply interpolating ln (T) data alone these results suggest that temperature measurements are a promising data source for site characterization for heterogeneous aquifer, which can be accomplished through the full-Bayesian methodology.
NASA Technical Reports Server (NTRS)
Liou, J.; Tezduyar, T. E.
1990-01-01
Adaptive implicit-explicit (AIE), grouped element-by-element (GEBE), and generalized minimum residuals (GMRES) solution techniques for incompressible flows are combined. In this approach, the GEBE and GMRES iteration methods are employed to solve the equation systems resulting from the implicitly treated elements, and therefore no direct solution effort is involved. The benchmarking results demonstrate that this approach can substantially reduce the CPU time and memory requirements in large-scale flow problems. Although the description of the concepts and the numerical demonstration are based on the incompressible flows, the approach presented here is applicable to larger class of problems in computational mechanics.
NASA Technical Reports Server (NTRS)
Liou, J.; Tezduyar, T. E.
1990-01-01
Adaptive implicit-explicit (AIE), grouped element-by-element (GEBE), and generalized minimum residuals (GMRES) solution techniques for incompressible flows are combined. In this approach, the GEBE and GMRES iteration methods are employed to solve the equation systems resulting from the implicitly treated elements, and therefore no direct solution effort is involved. The benchmarking results demonstrate that this approach can substantially reduce the CPU time and memory requirements in large-scale flow problems. Although the description of the concepts and the numerical demonstration are based on the incompressible flows, the approach presented here is applicable to larger class of problems in computational mechanics.
Do conservative and reactive tracers take the same water flow pathways? An experimental approach
NASA Astrophysics Data System (ADS)
Kasteel, Roy; Koestel, Johannes; Vereecken, Harry
2010-05-01
Reactive transport modelling heavily relies on the assumption that the soil's hydraulic behavior, i.e. the solute transport volume (water content) and the water flow pathways (dispersivity), can be characterized by the use of a conservative tracer. However, there exits ample experimental evidence in the literature whether this assumption holds, mainly because of the lack of detection methods that are able to monitor solute transport with a high resolution in space and time. Time-lapse electrical resistivity tomography (ERT) supplies three-dimensional spatio-temporally resolved image data through minimally invasive measurements. ERT has proved to be a valuable tool for imaging solute transport processes in the subsurface and has the potential to resolve the above-mentioned issue. The goals of this study are to verify to what extent ERT can be used to compare flow pathways of a conservative tracer (chloride) and a reactive tracer (food-dye Brilliant Blue) in the same large soil monolith filled with an undisturbed loamy sand and eventually address the question whether they take the same flow pathways. A constant water flow field was established in the soil monolith by means of an irrigation device. The tracers chloride and Brilliant Blue were successively added to the irrigation water. The negative charge of both tracer provides an electrical conductivity contrast that can be detected by means of ERT. Time-lapse ERT provides a qualitative comparison between both tracers, by visualizing the three-dimensional transport behavior. A quantitative analysis was performed by parameterizing the voxel-scale breakthrough curves using the convection-dispersion equation, which includes retardation and sorption kinetics for the reactive tracer. At the voxel-scale, heterogeneous water flow was observed, identified by regions with different pore-water velocities. In the subsoil, these regions were aligned to soil structural features of the plough pan. We discuss the comparison of the
Hagendorfer, Harald; Kaegi, Ralf; Traber, Jacqueline; Mertens, Stijn F L; Scherrers, Roger; Ludwig, Christian; Ulrich, Andrea
2011-11-14
In this work we discuss about the method development, applicability and limitations of an asymmetric flow field flow fractionation (A4F) system in combination with a multi-detector setup consisting of UV/vis, light scattering, and inductively coupled plasma mass spectrometry (ICPMS). The overall aim was to obtain a size dependent-, element specific-, and quantitative method appropriate for the characterization of metallic engineered nanoparticle (ENP) dispersions. Thus, systematic investigations of crucial method parameters were performed by employing well characterized Au nanoparticles (Au-NPs) as a defined model system. For good separation performance, the A4F flow-, membrane-, and carrier conditions were optimized. To obtain reliable size information, the use of laser light scattering based detectors was evaluated, where an online dynamic light scattering (DLS) detector showed good results for the investigated Au-NP up to a size of 80 nm in hydrodynamic diameter. To adapt large sensitivity differences of the various detectors, as well as to guarantee long term stability and minimum contamination of the mass spectrometer a split-flow concept for coupling ICPMS was evaluated. To test for reliable quantification, the ICPMS signal response of ionic Au standards was compared to that of Au-NP. Using proper stabilization with surfactants, no difference for concentrations of 1-50 μg Au L(-1) in the size range from 5 to 80 nm for citrate stabilized dispersions was observed. However, studies using different A4F channel membranes showed unspecific particle-membrane interaction resulting in retention time shifts and unspecific loss of nanoparticles, depending on the Au-NP system as well as membrane batch and type. Thus, reliable quantification and discrimination of ionic and particular species was performed using ICPMS in combination with ultracentrifugation instead of direct quantification with the A4F multi-detector setup. Figures of merit were obtained, by comparing the
A massively parallel computational approach to coupled thermoelastic/porous gas flow problems
NASA Technical Reports Server (NTRS)
Shia, David; Mcmanus, Hugh L.
1995-01-01
A new computational scheme for coupled thermoelastic/porous gas flow problems is presented. Heat transfer, gas flow, and dynamic thermoelastic governing equations are expressed in fully explicit form, and solved on a massively parallel computer. The transpiration cooling problem is used as an example problem. The numerical solutions have been verified by comparison to available analytical solutions. Transient temperature, pressure, and stress distributions have been obtained. Small spatial oscillations in pressure and stress have been observed, which would be impractical to predict with previously available schemes. Comparisons between serial and massively parallel versions of the scheme have also been made. The results indicate that for small scale problems the serial and parallel versions use practically the same amount of CPU time. However, as the problem size increases the parallel version becomes more efficient than the serial version.
Shukla, Chinmay A
2017-01-01
The implementation of automation in the multistep flow synthesis is essential for transforming laboratory-scale chemistry into a reliable industrial process. In this review, we briefly introduce the role of automation based on its application in synthesis viz. auto sampling and inline monitoring, optimization and process control. Subsequently, we have critically reviewed a few multistep flow synthesis and suggested a possible control strategy to be implemented so that it helps to reliably transfer the laboratory-scale synthesis strategy to a pilot scale at its optimum conditions. Due to the vast literature in multistep synthesis, we have classified the literature and have identified the case studies based on few criteria viz. type of reaction, heating methods, processes involving in-line separation units, telescopic synthesis, processes involving in-line quenching and process with the smallest time scale of operation. This classification will cover the broader range in the multistep synthesis literature. PMID:28684977
NASA Astrophysics Data System (ADS)
Hayat, Tasawar; Ijaz Khan, Muhammad; Imtiaz, Maria; Alsaedi, Ahmed; Waqas, Muhammad
2016-10-01
A simple model of chemical reactions for two dimensional ferrofluid flows is constructed. The impact of magnetic dipole and mixed convection is further analyzed. Flow is caused by linear stretching of the sheet. Similarity transformation is adopted to convert the partial differential equations into ordinary differential equations and then solved by Euler's explicit method. The characteristics of sundry parameters on the velocity, temperature, and concentration fields are graphically elaborated. It is noted that the impact of magneto-thermomechanical interaction is to slow down the fluid motion. The skin friction coefficient enhances and affects the rate of heat transfer. For higher values of ferrohydrodynamics, the interaction velocity shows decreasing behavior. Further the Prandtl number on temperature has opposite behavior when compared with thermal radiation and ferrohydrodynamics interaction.
A Finite-Element Approach for Modeling Inviscid and Viscous Compressible Flows using Prismatic Grids
NASA Technical Reports Server (NTRS)
Pandya, S. A.; Hefez, M.
2000-01-01
The Galerkin finite-element method is used to solve the Euler and Navier-Stokes equations on prismatic meshes. It is shown that the prismatic grid is advantageous for correctly and efficiently capturing the boundary layers in high Reynolds number flows. It can be captured accurately because of the ability to cluster grid points normal to the body. The efficiency derives from the implicit treatment of the normal direction. To treat the normal direction implicitly, a semi-implicit Runge-Kutta time stepping scheme is developed. The semi-implicit algorithm is validated on simple geometries for inviscid and viscous flows and its convergence history is compared to that of the explicit Runge-Kutta scheme. The semi-implicit scheme is shown to be a factor of 3 to 4 faster in terms of CPU time to convergence.
The design/analysis of flows through turbomachinery: A viscous/inviscid approach
NASA Technical Reports Server (NTRS)
Miller, D. P.; Reddy, D. R.
1991-01-01
The development of a design/analysis flow solver at NASA Lewis Research Center is discussed. The solver is axisymmetric and can be run inviscidly with assumed or calculated blockages, or with the viscous terms computed. The blade forces for each blade row are computed from blade-to-blade solutions, correlated data or force model, or from a full three dimensional solution. Codes currently under development can be separated into three distinct elements: the turbomachinery interactive grid generator energy distribution restart code (TIGGERC), the interactive blade element geometry generator (IBEGG), and the viscous/inviscid multi-blade-row average passage flow solver (VIADAC). Several experimental test cases were run to validate the VIADAC code. The tests, representative of typical axial turbomachinery duct axisymmetric wind tunnel body problems, were conducted on an SR7 Spinner axisymmetric body, a NASA Rotor 67 Fan test bed, and a transonic boatail body. The results show the computations to be in good agreement with test data.
NASA Astrophysics Data System (ADS)
Abraham, Theodore P.
2011-11-01
Hypertrophic Cardiomyopathy (HCM) is the most common inherited heart disease and occurs in 1 in 500 persons worldwide regardless of race, age and gender. It is the most common cause of sudden death in the young and also causes heart failure and cardiac arrhythmias. The primary anatomic abnormality is thickening of certain walls, or sometimes global thickening of the left or right ventricle. The patterns of thickening along with increased ventricular stiffness lead to suboptimal ventricular filling and inefficient ejection of blood from the ventricle. Treatment for HCM can be medical or surgical. The choice of therapy is driven by the presence and severity of outflow obstruction. Flow analysis could provide sophisticated information about outflow and inflow ventricular dynamics. These flow dynamics features may enable better medical choices and provide information that would allow superior surgical planning. Associate Professor of Medicine & Director, Hypertrophic Cardiomyopathy Clinic
A nonlinear optimization approach for UPFC power flow control and voltage security
NASA Astrophysics Data System (ADS)
Kalyani, Radha Padma
This dissertation provides a nonlinear optimization algorithm for the long term control of Unified Power Flow Controller (UPFC) to remove overloads and voltage violations by optimized control of power flows and voltages in the power network. It provides a control strategy for finding the long term control settings of one or more UPFCs by considering all the possible settings and all the (N-1) topologies of a power network. Also, a simple evolutionary algorithm (EA) has been proposed for the placement of more than one UPFC in large power systems. In this publication dissertation, Paper 1 proposes the algorithm and provides the mathematical and empirical evidence. Paper 2 focuses on comparing the proposed algorithm with Linear Programming (LP) based corrective method proposed in literature recently and mitigating cascading failures in larger power systems. EA for placement along with preliminary results of the nonlinear optimization is given in Paper 3.
Gasteiger, Rocco; Neugebauer, Mathias; Beuing, Oliver; Preim, Bernhard
2011-12-01
Blood flow and derived data are essential to investigate the initiation and progression of cerebral aneurysms as well as their risk of rupture. An effective visual exploration of several hemodynamic attributes like the wall shear stress (WSS) and the inflow jet is necessary to understand the hemodynamics. Moreover, the correlation between focus-and-context attributes is of particular interest. An expressive visualization of these attributes and anatomic information requires appropriate visualization techniques to minimize visual clutter and occlusions. We present the FLOWLENS as a focus-and-context approach that addresses these requirements. We group relevant hemodynamic attributes to pairs of focus-and-context attributes and assign them to different anatomic scopes. For each scope, we propose several FLOWLENS visualization templates to provide a flexible visual filtering of the involved hemodynamic pairs. A template consists of the visualization of the focus attribute and the additional depiction of the context attribute inside the lens. Furthermore, the FLOWLENS supports local probing and the exploration of attribute changes over time. The FLOWLENS minimizes visual cluttering, occlusions, and provides a flexible exploration of a region of interest. We have applied our approach to seven representative datasets, including steady and unsteady flow data from CFD simulations and 4D PC-MRI measurements. Informal user interviews with three domain experts confirm the usefulness of our approach.
Perruche, Sylvain; Kleinclauss, François; Lienard, Agnès; Robinet, Eric; Tiberghien, Pierre; Saas, Philippe
2004-11-01
The monitoring of immune reconstitution in murine models of HC transplantation, using accurate and automated methods, is necessary in view of the recent developments of hematopoietic cell (HC) transplantation (including reduced intensity conditioning regimens) as well as emerging immunological concepts (such as the involvement of dendritic cells or regulatory T cells). Here, we describe the use of a single-platform approach based on flow cytometry and tubes that contain a defined number of microbeads to evaluate absolute blood cell counts in mice. This method, previously used in humans to quantify CD34+ stem cells or CD4+ T cells in HIV infected patients, was adapted for mouse blood samples. A CD45 gating strategy in this "lyse no wash" protocol makes it possible to discriminate erythroblasts or red blood cell debris from CD45+ leukocytes, thus avoiding cell loss. Tubes contain a lyophilized brightly fluorescent microbead pellet permitting the acquisition of absolute counts of leukocytes after flow cytometric analysis. We compared this method to determine absolute counts of circulating cells with another method combining Unopette reservoir diluted blood samples, hemocytometer, microscopic examination and flow cytometry. The sensitivity of this single-platform approach was evaluated in different situations encountered in allogeneic HC transplantation, including immune cell depletion after different conditioning regimens, activation status of circulating cells after transplantation, evaluation of in vivo cell depletion and hematopoietic progenitor mobilization in the periphery. This single-platform flow cytometric assay can also be proposed to standardize murine (or other mammalian species) leukocyte count determination for physiological, pharmacological/toxicological and diagnostic applications in veterinary practice.
Field, laboratory and numerical approaches to studying flow through mangrove pneumatophores
NASA Astrophysics Data System (ADS)
Chua, V. P.
2014-12-01
The circulation of water in riverine mangrove swamps is expected to be influenced by mangrove roots, which in turn affect the nutrients, pollutants and sediments transport in these systems. Field studies were carried out in mangrove areas along the coastline of Singapore where Avicennia marina and Sonneratia alba pneumatophore species are found. Geometrical properties, such as height, diameter and spatial density of the mangrove roots were assessed through the use of photogrammetric methods. Samples of these roots were harvested from mangrove swamps and their material properties, such as bending strength and Young's modulus were determined in the laboratory. It was found that the pneumatophores under hydrodynamic loadings in a mangrove environment could be regarded as fairly rigid. Artificial root models of pneumatophores were fabricated from downscaling based on field observations of mangroves. Flume experiments were performed and measurements of mean flow velocities, Reynolds stress and turbulent kinetic energy were made. The boundary layer formed over the vegetation patch is fully developed after x = 6 m with a linear mean velocity profile. High shear stresses and turbulent kinetic energy were observed at the interface between the top portion of the roots and the upper flow. The experimental data was employed to calibrate and validate three-dimensional simulations of flow in pneumatophores. The simulations were performed with the Delft3D-FLOW model, where the vegetation effect is introduced by adding a depth-distributed resistance force and modifying the k-ɛ turbulence model. The model-predicted profiles for mean velocity, turbulent kinetic energy and concentration were compared with experimental data. The model calibration is performed by adjusting the horizontal and vertical eddy viscosities and diffusivities. A skill assessment of the model is performed using statistical measures that include the Pearson correlation coefficient (r), the mean absolute error
Cold flow simulation of an internal combustion engine with vertical valves using layering approach
NASA Astrophysics Data System (ADS)
Martinas, G.; Cupsa, O. S.; Stan, L. C.; Arsenie, A.
2015-11-01
Complying with emission requirements and fuel consumption efficiency are the points which drive any development of internal combustion engine. Refinement of the process of combustion and mixture formation, together with in-cylinder flow refinement, is a requirement, valves and piston bowl and intake exhaust port design optimization is essential. In order to reduce the time for design optimization cycle it is used Computational Fluid Dynamics (CFD). Being time consuming and highly costly caring out of experiment using flow bench testing this methods start to become less utilized. Air motion inside the intake manifold is one of the important factors, which govern the engine performance and emission of multi-cylinder diesel engines. Any cold flow study on IC is targeting the process of identifying and improving the fluid flow inside the ports and the combustion chamber. This is only the base for an optimization process targeting to increase the volume of air accessing the combustion space and to increase the turbulence of the air at the end of the compression stage. One of the first conclusions will be that the valve diameter is a fine tradeoff between the need for a bigger diameter involving a greater mass of air filling the cylinder, and the need of a smaller diameter in order to reduce the blind zone. Here there is room for optimization studies. The relative pressure indicates a suction effect coming from the moving piston. The more the shape of the inlet port is smoother and the diameter of the piston is bigger, the aerodynamic resistance of the geometry will be smaller so that the difference of inlet port pressure and the pressure near to piston face will be smaller. Here again there is enough room for more optimization studies.
NASA Astrophysics Data System (ADS)
Dong, S.
2014-06-01
We present an effective outflow boundary condition, and an associated numerical algorithm, within the phase-field framework for dealing with two-phase outflows or open boundaries. The set of two-phase outflow boundary conditions for the phase-field and flow variables are designed to prevent the un-controlled growth in the total energy of the two-phase system, even in situations where strong backflows or vortices may be present at the outflow boundaries. We also present an additional boundary condition for the phase field function, which together with the usual Dirichlet condition can work effectively as the phase-field inflow conditions. The numerical algorithm for dealing with these boundary conditions is developed on top of a strategy for de-coupling the computations of all flow variables and for overcoming the performance bottleneck caused by variable coefficient matrices associated with variable density/viscosity. The algorithm contains special constructions, for treating the variable dynamic viscosity in the outflow boundary condition, and for preventing a numerical locking at the outflow boundaries for time-dependent problems. Extensive numerical tests with incompressible two-phase flows involving inflow and outflow boundaries demonstrate that, the two-phase outflow boundary conditions and the numerical algorithm developed herein allow for the fluid interface and the two-phase flow to pass through the outflow or open boundaries in a smooth and seamless fashion, and that our method produces stable simulations when large density ratios and large viscosity ratios are involved and when strong backflows are present at the outflow boundaries.
Bluestein, Danny
2004-09-01
The advent of implantable blood recirculating devices has provided life-saving solutions to patients with severe cardiovascular diseases. Recently it has been reported that ventricular assist devices are superior to drug therapy. The implantable total artificial heart is showing promise as a potential solution to the chronic shortage of available heart transplants. Prosthetic heart valves are routinely used for replacing diseased heart valves. However, all of these devices share a common problem--significant complications such as hemolysis and thromboembolism often arise after their implantation. Elevated flow stresses that are present in the nonphysiologic geometries of blood recirculating devices, enhance their propensity to initiate thromboembolism by chronically activating the blood platelets. This, rather than hemolysis, appears to be the salient aspect of blood trauma in devices. Limitations in characterizing and controlling relevant aspects of the flow-induced mechanical stimuli and the platelet response, hampers our ability to achieve design optimization for these devices. The main objective of this article is to describe state-of-the-art numerical, experimental, and in vivo tools, that facilitate elucidation of flow-induced mechanisms leading to thromboembolism in prosthetic devices. Such techniques are giving rise to an accountable model for flow-induced thrombogenicity, and to a methodology that has the potential to transform current device design and testing practices. It might lead to substantial time and cost savings during the research and development phase, and has the potential to reduce the risks that patients implanted with these devices face, lower the ensuing healthcare costs, and offer viable long-term solutions for these patients.
Continuum Approaches for Describing Solid-Gas and Solid-Liquid Flow
1992-02-01
architecture, cellular automata , etc.) as they become available. These computer simulations can be used to evaluate the rheological properties and, hence, be...avalanches and sand- dune formation, in addition to its relevance for solid transport e.g., circulating fluidized beds. Simple kinetic theories of particle...Real flowing sand forms sandpiles (or sand dunes ) stabilized by sliding friction as the velocity becomes small, yet a continuum fluid model of the
A flow cytometric approach to the study of crustacean cellular immunity
Cardenas, W.; Jenkins, J.A.; Dankert, J.R.
2000-01-01
Responses of hemocytes from the crayfish Procambarus zonangulus to stimulation by fungal cell walls (Zymosan A) were measured by flow cytometry. Changes in hemocyte physical characteristics were assessed flow cytometrically using forward- and sidescatter light parameters, and viability was measured by two-color fluorescent staining with calcein-AM and ethidium homodimer 1. The main effects of zymosan A on crayfish hemocytes were reduction in cell size and viability compared to control mixtures (hemocytes in buffer only). Adding diethyldithiocarbamic acid, an inhibitor of phenoloxidase, to hemocyte to zymosan mixtures delayed the time course of cell size reduction and cell death compared to zymosan-positive controls. The inclusion of trypsin inhibitor in reaction mixtures further delayed the reduction in hemocyte size and cell death, thereby indicating that a proteolytic cascade, along with prophenoloxidase activation, played a key role in generating signal molecules which mediate these cellular responses. In addition to traditional methods such as microscopy and protein chemistry, flow cytometry can provide a simple, reproducible, and sensitve method for evaluating invertebrate hemocyte responses to immunological stimuli.
Effects of modified pharmacologic stress approaches on hyperemic myocardial blood flow
Czernin, J.; Auerbach, M.; Sun, K.T.
1995-04-01
Pharmacologic stress testing with 0.56 mg/kg of intravenous dipyridamole is frequently used to noninvasively detect coronary artery disease (CAD). However, high-dose dipyridamole (0.80 mg/kg) or the combination of standard-dose dipyridamole (0.56 mg/kg) with the isometric handgrip maneuver might evoke a greater coronary hyperemic response. To evaluate the effect of modified pharmacologic stress tests, myocardial blood flow was quantified in 11 male subjects (mean age: 27 {plus_minus} 7 yr) during standard-dose dipyridamole (0.56 mg/kg), high-dose dipyridamole (0.80 mg/kg) and standard-dose dipyridamole combined with the isometric handgrip exercise using dynamic PET and a two-compartment model for {sup 13}N-ammonia. Systolic blood pressure, heart rate and rate pressure product remained unchanged from standard to high-dose dipyridamole but increased with the addition of the isometric handgrip. Myocardial blood flow was unchanged from standard to high-dose dipyridamole but was lower with the addition of the isometric handgrip. The hyperemic response induced by standard-dose dipyridamole cannot be further enhanced by high-dose dipyridamole. The addition of the isometric handgrip exercise results in a modest, but significant decline in hyperemic blood flow possibly due to increased extravascular resistive forces or an increase in a mediated coronary vasoconstriction associated with exercise. 31 refs., 2 figs., 1 tab.
A first-order time-domain Green's function approach to supersonic unsteady flow
NASA Technical Reports Server (NTRS)
Freedman, M. I.; Tseng, K.
1985-01-01
A time-domain Green's Function Method for unsteady supersonic potential flow around complex aircraft configurations is presented. The focus is on the supersonic range wherein the linear potential flow assumption is valid. The Green's function method is employed in order to convert the potential-flow differential equation into an integral one. This integral equation is then discretized, in space through standard finite-element technique, and in time through finite-difference, to yield a linear algebraic system of equations relating the unknown potential to its prescribed co-normalwash (boundary condition) on the surface of the aircraft. The arbitrary complex aircraft configuration is discretized into hyperboloidal (twisted quadrilateral) panels. The potential and co-normalwash are assumed to vary linearly within each panel. Consistent with the spatial linear (first-order) finite-element approximations, the potential and co-normalwash are assumed to vary linearly in time. The long range goal of our research is to develop a comprehensive theory for unsteady supersonic potential aerodynamics which is capable of yielding accurate results even in the low supersonic (i.e., high transonic) range.
Approaches to myosin modelling in a two-phase flow model for cell motility
NASA Astrophysics Data System (ADS)
Kimpton, L. S.; Whiteley, J. P.; Waters, S. L.; Oliver, J. M.
2016-04-01
A wide range of biological processes rely on the ability of cells to move through their environment. Mathematical models have been developed to improve our understanding of how cells achieve motion. Here we develop models that explicitly track the cell's distribution of myosin within a two-phase flow framework. Myosin is a small motor protein which is important for contracting the cell's actin cytoskeleton and enabling cell motion. The two phases represent the actin network and the cytosol in the cell. We start from a fairly general description of myosin kinetics, advection and diffusion in the two-phase flow framework, then identify a number of sub-limits of the model that may be relevant in practice, two of which we investigate further via linear stability analyses and numerical simulations. We demonstrate that myosin-driven contraction of the actin network destabilizes a stationary steady state leading to cell motion, but that rapid diffusion of myosin and rapid unbinding of myosin from the actin network are stabilizing. We use numerical simulation to investigate travelling-wave solutions relevant to a steadily gliding cell and we consider a reduction of the model in which the cell adheres strongly to the substrate on which it is crawling. This work demonstrates that a number of existing models for the effect of myosin on cell motility can be understood as different sub-limits of our two-phase flow model.
Biomimetic approaches for green tribology: from the lotus effect to blood flow control
NASA Astrophysics Data System (ADS)
Maani, Nazanin; Rayz, Vitaliy S.; Nosonovsky, Michael
2015-09-01
The research in Green tribology combines several areas including biomimetic tribomaterials and surfaces for controlled adhesion. Biomimetic surfaces mimic living nature and thus they are eco-friendly. The most famous biomimetic surface effect is the Lotus effect (reduction of water adhesion to a solid surface due to micro/nanostructuring of the solid surface). Several extensions of the Lotus effect have been discussed in the literature including the oleophobicity (repelling organic liquids such as oils), underwater oleophobicity to reduce fouling, and the shark skin effect (flow drag reduction due to specially oriented micro-riblets). Here we suggest a potentially important application of micro/nanostructured surfaces in the biomedical area: the micro/nanostructure controlled adhesion in blood flow. Blood is a suspension, and its adhesion properties are different from those of water and oil. For many cardiovascular applications, it is desirable to reduce stagnation and clotting of blood. Therefore, both the underwater oleophobicuity and shark-skin effect can be used. We discuss how computational fluid dynamics models can be used to investigate the structure-property relationships of surface pattern-controlled blood flow adhesion.
Estimation of flow properties using surface deformation and head data: A trajectory-based approach
Vasco, D.W.
2004-07-12
A trajectory-based algorithm provides an efficient and robust means to infer flow properties from surface deformation and head data. The algorithm is based upon the concept of an ''arrival time'' of a drawdown front, which is defined as the time corresponding to the maximum slope of the drawdown curve. The technique involves three steps: the inference of head changes as a function of position and time, the use of the estimated head changes to define arrival times, and the inversion of the arrival times for flow properties. Trajectories, computed from the output of a numerical simulator, are used to relate the drawdown arrival times to flow properties. The inversion algorithm is iterative, requiring one reservoir simulation for each iteration. The method is applied to data from a set of 14 tiltmeters, located at the Raymond Quarry field site in California. Using the technique, I am able to image a high-conductivity channel which extends to the south of the pumping well. The presence of th is permeable pathway is supported by an analysis of earlier cross-well transient pressure test data.
An ALE Finite Element Approach for Two-Phase Flow with Phase Change
NASA Astrophysics Data System (ADS)
Gros, Erik; Anjos, Gustavo; Thome, John; Ltcm Team; Gesar Team
2016-11-01
In this work, two-phase flow with phase change is investigated through the Finite Element Method (FEM) in the Arbitrary Lagrangian-Eulerian (ALE) framework. The equations are discretized on an unstructured mesh where the interface between the phases is explicitly defined as a sub-set of the mesh. The two-phase interface position is described by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to very accurate results with moderate programming effort and computational costs. Such a methodology can be employed to study accurately many two-phase flow and heat transfer problems in industry such as oil extraction and refinement, design of refrigeration systems, modelling of microfluidic and biological systems and efficient cooling of electronics for computational purposes. The latter is the principal aim of the present research. The numerical results are discussed and compared to analytical solutions and reference results, thereby revealing the capability of the proposed methodology as a platform for the study of two-phase flow with phase change.
NASA Astrophysics Data System (ADS)
von Larcher, Thomas; Blome, Therese; Klein, Rupert; Schneider, Reinhold; Wolf, Sebastian; Huber, Benjamin
2016-04-01
Handling high-dimensional data sets like they occur e.g. in turbulent flows or in multiscale behaviour of certain types in Geosciences are one of the big challenges in numerical analysis and scientific computing. A suitable solution is to represent those large data sets in an appropriate compact form. In this context, tensor product decomposition methods currently emerge as an important tool. One reason is that these methods often enable one to attack high-dimensional problems successfully, another that they allow for very compact representations of large data sets. We follow the novel Tensor-Train (TT) decomposition method to support the development of improved understanding of the multiscale behavior and the development of compact storage schemes for solutions of such problems. One long-term goal of the project is the construction of a self-consistent closure for Large Eddy Simulations (LES) of turbulent flows that explicitly exploits the tensor product approach's capability of capturing self-similar structures. Secondly, we focus on a mixed deterministic-stochastic subgrid scale modelling strategy currently under development for application in Finite Volume Large Eddy Simulation (LES) codes. Advanced methods of time series analysis for the databased construction of stochastic models with inherently non-stationary statistical properties and concepts of information theory based on a modified Akaike information criterion and on the Bayesian information criterion for the model discrimination are used to construct surrogate models for the non-resolved flux fluctuations. Vector-valued auto-regressive models with external influences form the basis for the modelling approach [1], [2], [4]. Here, we present the reconstruction capabilities of the two modeling approaches tested against 3D turbulent channel flow data computed by direct numerical simulation (DNS) for an incompressible, isothermal fluid at Reynolds number Reτ = 590 (computed by [3]). References [1] I
A Bayesian Hierarchical Modeling Approach to Predicting Flow in Ungauged Basins
Recent innovative approaches to identifying and applying regression-based relationships between land use patterns (such as increasing impervious surface area and decreasing vegetative cover) and rainfall-runoff model parameters represent novel and promising improvements to predic...
A Bayesian Hierarchical Modeling Approach to Predicting Flow in Ungauged Basins
Recent innovative approaches to identifying and applying regression-based relationships between land use patterns (such as increasing impervious surface area and decreasing vegetative cover) and rainfall-runoff model parameters represent novel and promising improvements to predic...
NASA Astrophysics Data System (ADS)
Goswami, M.; O'Connor, K. M.; Bhattarai, K. P.
2007-02-01
SummaryFlow simulation in ungauged catchments is presently regarded as one of the most challenging tasks in surface water hydrology. Many of the ungauged catchments are located in the headwaters of rivers in mountainous regions of the world having enormous potential for sustainable water resource development. However, due to inaccessibility, rugged and inhospitable terrain, and historical lack of foresight concerning the need to have these headwaters adequately gauged, their potential is not readily realizable. Many downstream sites also suffer from non-availability of site-specific data as even in countries having extensive networks of gauged stations data may not be available at sites where these are most needed. As predictive tools for water resources, water quality, natural hazard mitigation and water availability assessment are generally data-driven, the lack of adequate hydrometric records poses difficult problems for planners, engineers, managers, and stake-holders alike. In this study, a methodology is developed for flow simulation in ungauged catchments using a regionalisation and multi-model approach involving a suite of rainfall-runoff models and combination techniques. Daily observed hydrometeorological data for 12 French catchments are used for illustrating the procedures. Following a preliminary investigation of the regional homogeneity of that group of catchments, three regional flow simulation techniques are applied. Although all 12 catchments are gauged, initially each catchment is successively considered as being ungauged for the purpose of flow simulation in that catchment, their actual discharges being subsequently used for evaluating the performance of the flow estimation procedures for the catchment. The Nash-Sutcliffe efficiency index ( R2) is used for assessing and ranking the relative performances of the regionalisation-model couples to identify the most appropriate couple for the region. The final step of applying that couple to a truly
Essaid, H.I.
1986-01-01
A quasi-three dimensional finite difference model which simulates coupled, fresh water and salt water flow, separated by a sharp interface, is used to investigate the effects of storage characteristics, transmissivity, boundary conditions and anisotropy on the transient responses of such flow systems. The magnitude and duration of the departure of aquifer response from the behavior predicted using the Ghyben-Herzberg, one-fluid approach is a function of the ease with which flow can be induced in the salt water region. In many common hydrogeologic settings short-term fresh water head responses, and transitional responses between short-term and long-term, can only be realistically reproduced by including the effects of salt water flow on the dynamics of coastal flow systems. The coupled fresh water-salt water flow modeling approach is able to reproduce the observed annual fresh water head response of the Waialae aquifer of southeastern Oahu, Hawaii. ?? 1986.
2011-01-01
Homogeneous Condensation in High Density Gas Expansions (Postprint) 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Ryan Jansen ...Prescribed by ANSI Std. 239.18 A Lagrangian–Eulerian approach to modeling homogeneous condensation in high density gas expansions Ryan Jansen , Natalia...Lagrangian–Eulerian approach to modeling homogeneous condensation in high density gas expansions Ryan Jansen ,1 Natalia Gimelshein,2 Sergey Gimelshein,2
NASA Astrophysics Data System (ADS)
Pioli, L.; Azzopardi, B. J.; Bonadonna, C.; Marchetti, E.; Ripepe, M.
2009-12-01
Open conduit basaltic volcanoes are characterized by frequent eruptions, usually consisting in mild Strombolian and Hawaiian explosions, alternating years to months of quiescence periods, with degassing activity from the central conduit. Recent improvements of thermal, video, radar and acoustic monitoring techniques have provided new powerful tools for the study of degassing processes and made available geophysical and geochemical datasets for many central volcanoes, such as Stromboli, Etna (Italy), Kilauea (Hawaii), Villarrica (Chile). These studies revealed that degassing is an unsteady, often pulsatory process, characterized by fluctuations in both intensity and composition of the emitted gases. Unambiguous interpretation of monitoring data of surface activity in terms of conduit dynamics and flow processes is, however, not possible, due to partial knowledge of the physical processes controlling the dynamics of two-phase flows in magmas. We performed a series of experiments to gain further insights on the dynamics of the gas-bubble rise in magmas within a cylindrical conduit, their ability to segregate and coalesce and the effect of these processes on the degassing dynamics. The experiments consisted in generating fluxes at variable intensities of air through stagnant water or glucose syrup in a bubble column apparatus 6.5 m high and with a diameter of 24 cm diameter. Glucose syrup and water are Newtonian liquids with viscosity ranging from 2.4 to 204.0 Pa*s and from 1.7 to 0.2 10 -3 Pa*s respectively, depending on temperature. Air was inserted at the base of the column through a variable number (1 to 25) of 5mm-diameter nozzles reaching surficial gas velocities of up to 0.5 m/s. The activity of the bubble column was monitored through temperature, pressure, void fraction and acoustic measurements and filmed by a high-speed camera with maximum resolution of 800x600 pixels. Pressure fluctuations, vesicularity and acoustic signal were then analyzed and correlated
NASA Astrophysics Data System (ADS)
Miller, J. D.; Rickards, N. J.; Kjeldsen, T. R.; Hutchins, M.; Rowland, C.; Prudhomme, C.; Maliko, T.; Fidal, J.; Hagen-Zanker, A.
2016-12-01
The UK population is set to increase by 16% by 2035; it is therefore increasingly important to understand the impact this may have on urban populations, and in turn how this will affect river flow regimes and water quality in urban areas. A growing population is likely to lead to an increase in urban land use and impervious surfaces, the implications of which are not yet fully understood for issues such as future flood risk. The aim of this paper is to develop a greater understanding of the impacts of both an increasing population and urban extent in the context of a changing climate, and to assess the effect these may have on urban streamflow regimes and water security in the future. Flows are modelled for selected catchments in the Thames basin using URBMOD, a lumped rainfall runoff model that is able to represent both pervious and impervious surfaces, reducing infiltration in catchments where there is a greater urban extent. The model uses daily catchment average rainfall and evapotranspiration derived from gridded data, and is calibrated against long-term river flow records. Historic satellite imagery is used to train cellular automata land use models, which are then applied under different scenarios of urban development up to 2035. These changes in land use are combined with a range of climate change scenarios to give an indication of how urban flow regimes may be altered in the Thames basin over the next 20 years. Results suggest an intensification of the hydrological regime in the majority of catchments, with increases in high flow magnitudes (Q10) of up to 5%. The trend for low flows (Q90) is less clear, with some catchments displaying reductions of around 4%, whilst others show slight increased flows. We identify the main drivers behind these changes, from which the fine-scale impacts of urbanisation on water resources can be better understood. Research findings are being used to inform a regional-scale model, coupling water quantity and quality and
A regression approach to the analysis of serial peak flow among fuel oil ash exposed workers.
Hauser, R; Daskalakis, C; Christiani, D C
1996-10-01
We investigated the association between exposure to fuel oil ash and acute airway obstruction in 31 boilermakers and 31 utility workers during the overhaul of a large oil-fired boiler. Air flow was assessed with self-recorded serial peak expiratory flow rate measurements (PEFR) using a mini-Wright meter. Exposure to thoracic particulates with an aerodynamic diameter of 10 gm or smaller (PM10) was assessed using personal sampling devices and detailed work diaries. All subjects were male, with an average age of 43 yr, and an average of 18 yr at their current trade. Average PM10 exposure on work days was 2.75 mg/m3 for boilermakers and 0.57 mg/m3 for utility workers. Three daily PEFR measurements (start-of-shift, end-of-shift, and bed-time) were analyzed simultaneously, using Huber linear regression. After adjustment for job title, welder status, age, height, smoking, and weld-years, for each mg/m3 increase in PM10, the estimated decline in PEFR was 13.2 L/min (p = 0.008) for end-of-shift, 9.9 L/min (p = 0.045) for bed-time, and 6.6 L/min (p = 0.26) for start-of-shift of the following day. This decline of the exposure effect over the 24-h period that follows was statistically significant (p = 0.004). No other factors were found to significantly modify the effect of exposure. Our results suggest that occupational exposure to fuel oil ash is associated with significant acute decrements in peak flow.
NASA Astrophysics Data System (ADS)
Besse, Nicolas; Frisch, Uriel
2017-04-01
The 3D incompressible Euler equations are an important research topic in the mathematical study of fluid dynamics. Not only is the global regularity for smooth initial data an open issue, but the behaviour may also depend on the presence or absence of boundaries. For a good understanding, it is crucial to carry out, besides mathematical studies, high-accuracy and well-resolved numerical exploration. Such studies can be very demanding in computational resources, but recently it has been shown that very substantial gains can be achieved first, by using Cauchy's Lagrangian formulation of the Euler equations and second, by taking advantage of analyticity results of the Lagrangian trajectories for flows whose initial vorticity is Hölder-continuous. The latter has been known for about 20 years (Serfati in J Math Pures Appl 74:95-104, 1995), but the combination of the two, which makes use of recursion relations among time-Taylor coefficients to obtain constructively the time-Taylor series of the Lagrangian map, has been achieved only recently (Frisch and Zheligovsky in Commun Math Phys 326:499-505, 2014; Podvigina et al. in J Comput Phys 306:320-342, 2016 and references therein). Here we extend this methodology to incompressible Euler flow in an impermeable bounded domain whose boundary may be either analytic or have a regularity between indefinite differentiability and analyticity. Non-constructive regularity results for these cases have already been obtained by Glass et al. (Ann Sci Éc Norm Sup 45:1-51, 2012). Using the invariance of the boundary under the Lagrangian flow, we establish novel recursion relations that include contributions from the boundary. This leads to a constructive proof of time-analyticity of the Lagrangian trajectories with analytic boundaries, which can then be used subsequently for the design of a very high-order Cauchy-Lagrangian method.
Zaccariello, Lucio; Cremiato, Raffaele; Mastellone, Maria Laura
2015-10-01
The main role of a waste management plan is to define which is the combination of waste management strategies and method needed to collect and manage the waste in such a way to ensure a given set of targets is reached. Objectives have to be sustainable and realistic, consistent with the environmental policies and regulations and monitored to verify the progressive achievement of the given targets. To get the aim, the setting up and quantification of indicators can allow the measurement of efficiency of a waste management system. The quantification of efficiency indicators requires the developing of a material flow analysis over the system boundary, from waste collection to secondary materials selling, processing and disposal. The material flow analysis has been carried out with reference to a case study for which a reliable, time- and site-specific database was available. The material flow analysis allowed the evaluation of the amount of materials sent to recycling, to landfilling and to waste-to-energy, by highlighting that the sorting of residual waste can further increase the secondary materials amount. The utilisation of energy recovery to treat the low-grade waste allows the maximisation of waste diversion from landfill with a low production of hazardous ash. A preliminary economic balance has been carried out to define the gate fee of the waste management system that was in the range of 84-145 € t(-1) without including the separate collection cost. The cost of door-by-door separate collection, designed to ensure the collection of five separate streams, resulted in 250 € t(-1) ±30%. © The Author(s) 2015.
NASA Astrophysics Data System (ADS)
Besse, Nicolas; Frisch, Uriel
2017-01-01
The 3D incompressible Euler equations are an important research topic in the mathematical study of fluid dynamics. Not only is the global regularity for smooth initial data an open issue, but the behaviour may also depend on the presence or absence of boundaries. For a good understanding, it is crucial to carry out, besides mathematical studies, high-accuracy and well-resolved numerical exploration. Such studies can be very demanding in computational resources, but recently it has been shown that very substantial gains can be achieved first, by using Cauchy's Lagrangian formulation of the Euler equations and second, by taking advantage of analyticity results of the Lagrangian trajectories for flows whose initial vorticity is Hölder-continuous. The latter has been known for about 20 years (Serfati in J Math Pures Appl 74:95-104, 1995), but the combination of the two, which makes use of recursion relations among time-Taylor coefficients to obtain constructively the time-Taylor series of the Lagrangian map, has been achieved only recently (Frisch and Zheligovsky in Commun Math Phys 326:499-505, 2014; Podvigina et al. in J Comput Phys 306:320-342, 2016 and references therein). Here we extend this methodology to incompressible Euler flow in an impermeable bounded domain whose boundary may be either analytic or have a regularity between indefinite differentiability and analyticity. Non-constructive regularity results for these cases have already been obtained by Glass et al. (Ann Sci Éc Norm Sup 45:1-51, 2012). Using the invariance of the boundary under the Lagrangian flow, we establish novel recursion relations that include contributions from the boundary. This leads to a constructive proof of time-analyticity of the Lagrangian trajectories with analytic boundaries, which can then be used subsequently for the design of a very high-order Cauchy-Lagrangian method.
FISH-Flow: a quantitative molecular approach for describing mixed clade communities of Symbiodinium
NASA Astrophysics Data System (ADS)
McIlroy, S. E.; Smith, G. J.; Geller, J. B.
2014-03-01
Our understanding of reef corals and their fate in a changing climate is limited by our ability to monitor the diversity and abundance of the dinoflagellate endosymbionts that sustain them. This study combined two well-known methods in tandem: fluorescent in situ hybridization (FISH) for genotype-specific labeling of Symbiodinium and flow cytometry to quantify the abundance of each symbiont clade in a sample. This technique (FISH-Flow) was developed with cultured Symbiodinium representing four distinct clades (based on large subunit rDNA) and was used to distinguish and quantify these types with high efficiency and few false positives. This technique was also applied to freshly isolated symbionts of Orbicella faveolata and Orbicella annularis. Isolates from acutely bleached coral tissues had significantly lower labeling efficiency; however, isolates from healthy tissue had efficiencies comparable to cultured Symbiodinium trials. RNA degradation in bleaching samples may have interfered with labeling of cells. Nevertheless, we were able to determine that, with and without thermal stress, experimental columns of the coral O. annularis hosted a majority of clade B and B/C symbionts on the top and side of the coral column, respectively. We demonstrated that, for cultured Symbiodinium and Symbiodinium freshly isolated from healthy host tissues, the relative ratio of clades could be accurately determined for clades present at as low as 7 % relative abundance. While this method does not improve upon PCR-based techniques in identifying clades at background levels, FISH-Flow provides a high precision, flexible system for targeting, quantifying and isolating Symbiodinium genotypes of interest.
Field-tracing approach to determine flow velocity and hydraulic conductivity in saturated peat soils
Gafni, A.
1986-01-01
A tracing methodology based on the point dilution concept was developed to quantify groundwater velocities in saturated peat soils. Groundwater velocity was measured in four different peatlands. The steepest hydraulic gradient and the dominant direction of groundwater flow were determined for each peatland. The hydraulic conductivity (K) of selected peat layers was estimated from measured groundwater velocity and hydraulic gradient using Darcy's equation. The effective porosity of three peat layers was determined using the pressure plate technique. The estimated hydraulic parameters of one of the bags were further evaluated by analyzing a rainfall-runoff event that exhibited groundwater discharge.
Enhancing Knowledge Flow in a Health Care Context: A Mobile Computing Approach
Souza, Diego Da Silva; de Lima, Patrícia Zudio; da Silveira, Pedro C; de Souza, Jano Moreira
2014-01-01
Background Advances in mobile computing and wireless communication have allowed people to interact and exchange knowledge almost anywhere. These technologies support Medicine 2.0, where the health knowledge flows among all involved people (eg, patients, caregivers, doctors, and patients’ relatives). Objective Our paper proposes a knowledge-sharing environment that takes advantage of mobile computing and contextual information to support knowledge sharing among participants within a health care community (ie, from patients to health professionals). This software environment enables knowledge exchange using peer-to-peer (P2P) mobile networks based on users’ profiles, and it facilitates face-to-face interactions among people with similar health interests, needs, or goals. Methods First, we reviewed and analyzed relevant scientific articles and software apps to determine the current state of knowledge flow within health care. Although no proposal was capable of addressing every aspect in the Medicine 2.0 paradigm, a list of requirements was compiled. Using this requirement list and our previous works, a knowledge-sharing environment was created integrating Mobile Exchange of Knowledge (MEK) and the Easy to Deploy Indoor Positioning System (EDIPS), and a twofold qualitative evaluation was performed. Second, we analyzed the efficiency and reliability of the knowledge that the integrated MEK-EDIPS tool provided to users according to their interest topics, and then performed a proof of concept with health professionals to determine the feasibility and usefulness of using this solution in a real-world scenario. Results . Using MEK, we reached 100% precision and 80% recall in the exchange of files within the peer-to-peer network. The mechanism that facilitated face-to-face interactions was evaluated by the difference between the location indicated by the EDIPS tool and the actual location of the people involved in the knowledge exchange. The average distance error was <6
Numerical experiments on breaking waves on contrasting beaches using a two-phase flow approach
NASA Astrophysics Data System (ADS)
Bakhtyar, R.; Barry, D. A.; Kees, C. E.
2012-11-01
A mechanistic understanding of beach environments needs to account for interactions of oceanic forcing and beach materials, in particular the role of waves on the evolution of the beach profile. A fully coupled two-phase flow model was used to simulate nearshore fluid-sediment turbulent flow in the cross-shore direction. It includes the Reynolds-Averaged Navier-Stokes equations and turbulent stress closures for each phase, and accounts for inter-granular stresses. The model has previously been validated using laboratory-scale data, so the results are likely more reliable for that scale. It was used to simulate wave breaking and the ensuing hydrodynamics and sediment transport processes in the surf/swash zones. Numerical experiments were conducted to investigate the effects of varying beach and wave characteristics (e.g., beach slope, sediment grain size, wave periods and heights) on the foreshore profile changes. Spilling and plunging breakers occur on dissipative and intermediate beaches, respectively. The impact of these wave/beach types on nearshore zone hydrodynamics and beach morphology was determined. The numerical results showed that turbulent kinetic energy, sediment concentrations and transport rate are greater on intermediate than on dissipative beaches. The results confirmed that wave energy, beach grain size and bed slope are main factors for sediment transport and beach morphodynamics. The location of the maximum sediment transport is near the breaking point for both beach types. Coarse- and fine-sand beaches differ significantly in their erosive characteristics (e.g., foreshore profile evolutions are erosive and accretionary on the fine and coarse sand beaches, respectively). In addition, a new parameter (based on main driving factors) is proposed that can characterize the sediment transport in the surf and swash zones. The results are consistent with existing physical observations, suggesting that the two-phase flow model is suitable for the
Enhancing knowledge flow in a health care context: a mobile computing approach.
Oliveira, Jonice; Souza, Diego Da Silva; de Lima, Patrícia Zudio; da Silveira, Pedro C; de Souza, Jano Moreira
2014-11-26
Advances in mobile computing and wireless communication have allowed people to interact and exchange knowledge almost anywhere. These technologies support Medicine 2.0, where the health knowledge flows among all involved people (eg, patients, caregivers, doctors, and patients' relatives). Our paper proposes a knowledge-sharing environment that takes advantage of mobile computing and contextual information to support knowledge sharing among participants within a health care community (ie, from patients to health professionals). This software environment enables knowledge exchange using peer-to-peer (P2P) mobile networks based on users' profiles, and it facilitates face-to-face interactions among people with similar health interests, needs, or goals. First, we reviewed and analyzed relevant scientific articles and software apps to determine the current state of knowledge flow within health care. Although no proposal was capable of addressing every aspect in the Medicine 2.0 paradigm, a list of requirements was compiled. Using this requirement list and our previous works, a knowledge-sharing environment was created integrating Mobile Exchange of Knowledge (MEK) and the Easy to Deploy Indoor Positioning System (EDIPS), and a twofold qualitative evaluation was performed. Second, we analyzed the efficiency and reliability of the knowledge that the integrated MEK-EDIPS tool provided to users according to their interest topics, and then performed a proof of concept with health professionals to determine the feasibility and usefulness of using this solution in a real-world scenario. . Using MEK, we reached 100% precision and 80% recall in the exchange of files within the peer-to-peer network. The mechanism that facilitated face-to-face interactions was evaluated by the difference between the location indicated by the EDIPS tool and the actual location of the people involved in the knowledge exchange. The average distance error was <6.28 m for an indoor environment. The
Huang, Jinhua; Su, Liang; Kowalski, Jeffrey A; Barton, John L.; Ferrandon, Magali; Burrell, Anthony K.; Brushett, Fikile R.; Zhang, Lu
2015-01-01
The development of new high capacity redox active materials is key to realizing the potential of non-aqueous redox flow batteries (RFBs). In this paper, a series of substituted 1,4- dimethoxybenzenes based redox active molecules, have been developed via a subtractive design approach. Five molecules have been proposed and developed by removing or reducing the bulky substituent groups of DBBB (2,5-di-tert-butyl-1,4- bis(2-methoxyethoxy)benzene), a successful overcharge protection material for lithium-ion batteries. Of these derivatives, 2,3-dimethyl-1,4-dimethoxybenzene (23DDB) and 2,5-dimethyl-1,4-dimethoxybenzene (25DDB) are particularly promising as they demonstrate favorable electrochemical characteristics at gravimetric capacities (161 mAh/g) that approach the stability limit of chemically reversible dimethoxybenzene based structures. Diffusivity, solubility, and galvanostatic cycling results indicate that both 23DDB and 25DDB molecules have promise for non-aqueous RFBs.
NASA Astrophysics Data System (ADS)
Lin, Yi-Kuei; Yeh, Cheng-Ta
2013-03-01
Many real-life systems, such as computer systems, manufacturing systems and logistics systems, are modelled as stochastic-flow networks (SFNs) to evaluate network reliability. Here, network reliability, defined as the probability that the network successfully transmits d units of data/commodity from an origin to a destination, is a performance indicator of the systems. Network reliability maximization is a particular objective, but is costly for many system supervisors. This article solves the multi-objective problem of reliability maximization and cost minimization by finding the optimal component assignment for SFN, in which a set of multi-state components is ready to be assigned to the network. A two-stage approach integrating Non-dominated Sorting Genetic Algorithm II and simple additive weighting are proposed to solve this problem, where network reliability is evaluated in terms of minimal paths and recursive sum of disjoint products. Several practical examples related to computer networks are utilized to demonstrate the proposed approach.
NASA Technical Reports Server (NTRS)
Daywitt, J.; Kutler, P.; Anderson, D.
1977-01-01
The technique of floating shock fitting is adapted to the computation of the inviscid flowfield about circular cones in a supersonic free stream at angles of attack that exceed the cone half-angle. The resulting equations are applicable over the complete range of free-stream Mach numbers, angles of attack and cone half-angles for which the bow shock is attached. A finite difference algorithm is used to obtain the solution by an unsteady relaxation approach. The bow shock, embedded cross-flow shock, and vortical singularity in the leeward symmetry plane are treated as floating discontinuities in a fixed computational mesh. Where possible, the flowfield is partitioned into windward, shoulder, and leeward regions with each region computed separately to achieve maximum computational efficiency. An alternative shock fitting technique which treats the bow shock as a computational boundary is developed and compared with the floating-fitting approach. Several surface boundary condition schemes are also analyzed.
Calculations of unsteady flows around high-lift configurations based on a zonal approach
NASA Astrophysics Data System (ADS)
Bosnyakov, S.; Kursakov, I.; Mikhaylov, S.; Vlasenko, V.
2015-06-01
Zonal approach for unsteady Reynolds-averaged Navier-Stokes (URANS) problem solution is described. Original feature of this approach is to use Courant-Friedrichs-Levi number CFL ˜ 1 in the main part of calculation domain excluding thin part of boundary layer. It is achieved by using explicit numerical scheme with fractional time stepping in the main part of calculation domain. In the near-wall zone of boundary layer, implicit dual stepping method is used. In addition to zonal approach, fully implicit method with dual stepping technology is also implemented. The methods are verified in comparison with the results of test case data obtained by consortium participants within DeSiReH FP-7 project.
Insect-Inspired Self-Motion Estimation with Dense Flow Fields--An Adaptive Matched Filter Approach.
Strübbe, Simon; Stürzl, Wolfgang; Egelhaaf, Martin
2015-01-01
The control of self-motion is a basic, but complex task for both technical and biological systems. Various algorithms have been proposed that allow the estimation of self-motion from the optic flow on the eyes. We show that two apparently very different approaches to solve this task, one technically and one biologically inspired, can be transformed into each other under certain conditions. One estimator of self-motion is based on a matched filter approach; it has been developed to describe the function of motion sensitive cells in the fly brain. The other estimator, the Koenderink and van Doorn (KvD) algorithm, was derived analytically with a technical background. If the distances to the objects in the environment can be assumed to be known, the two estimators are linear and equivalent, but are expressed in different mathematical forms. However, for most situations it is unrealistic to assume that the distances are known. Therefore, the depth structure of the environment needs to be determined in parallel to the self-motion parameters and leads to a non-linear problem. It is shown that the standard least mean square approach that is used by the KvD algorithm leads to a biased estimator. We derive a modification of this algorithm in order to remove the bias and demonstrate its improved performance by means of numerical simulations. For self-motion estimation it is beneficial to have a spherical visual field, similar to many flying insects. We show that in this case the representation of the depth structure of the environment derived from the optic flow can be simplified. Based on this result, we develop an adaptive matched filter approach for systems with a nearly spherical visual field. Then only eight parameters about the environment have to be memorized and updated during self-motion.
Insect-Inspired Self-Motion Estimation with Dense Flow Fields—An Adaptive Matched Filter Approach
Strübbe, Simon; Stürzl, Wolfgang; Egelhaaf, Martin
2015-01-01
The control of self-motion is a basic, but complex task for both technical and biological systems. Various algorithms have been proposed that allow the estimation of self-motion from the optic flow on the eyes. We show that two apparently very different approaches to solve this task, one technically and one biologically inspired, can be transformed into each other under certain conditions. One estimator of self-motion is based on a matched filter approach; it has been developed to describe the function of motion sensitive cells in the fly brain. The other estimator, the Koenderink and van Doorn (KvD) algorithm, was derived analytically with a technical background. If the distances to the objects in the environment can be assumed to be known, the two estimators are linear and equivalent, but are expressed in different mathematical forms. However, for most situations it is unrealistic to assume that the distances are known. Therefore, the depth structure of the environment needs to be determined in parallel to the self-motion parameters and leads to a non-linear problem. It is shown that the standard least mean square approach that is used by the KvD algorithm leads to a biased estimator. We derive a modification of this algorithm in order to remove the bias and demonstrate its improved performance by means of numerical simulations. For self-motion estimation it is beneficial to have a spherical visual field, similar to many flying insects. We show that in this case the representation of the depth structure of the environment derived from the optic flow can be simplified. Based on this result, we develop an adaptive matched filter approach for systems with a nearly spherical visual field. Then only eight parameters about the environment have to be memorized and updated during self-motion. PMID:26308839
Utilization of streamwise vortices to enhance mixing in supersonic 3D flows - Numerical approach
NASA Astrophysics Data System (ADS)
Yamasaki, Nobuhiko; Sakata, Nobuyasu; Namba, Masanobu
As one of the effective ways to enhance mixing of supersonic flows without increasing the loss, the utilization of the streamwise, i.e., axial vortices produced by the lobed splitter plate with wavy trailing edge has been proposed. The paper presents numerical solutions of the Reynolds-averaged Navier-Stokes equations to show the production of axial vortices and to discuss the effects of parameters on the overall flow and temperature fields. It is shown that the lobed plate gives thicker shear-layer than the flat plate does. In addition, the convoluted shear-layer at the downstream position of the lobed mixer plate is susceptible to breaking down and gives higher mixing efficiency. Although the streamwise vortices dissipate at downstream locations, the maximum vorticity in the vortex cell appears unchanged, and the vortex cell structure remains unaltered even at far downstream locations. Thus, the generated streamwise vortices are expected to realize the efficient mixing with the least loss in the shear-layer.
Cegelski, C C; Waits, L P; Anderson, N J
2003-11-01
In North America, wolverines once occupied a continuous range from Alaska southward to New Mexico. In the lower 48 states, small remnant populations remain only in the northwestern United States. Among these remnant populations, the Montana population has the highest probability of long-term persistence given its size and proximity to healthy populations in Canada. In this study, we evaluate population genetic structure and gene flow among Montana wolverines using 10 polymorphic microsatellite loci. Bayesian and frequency-based assignment tests revealed significant population substructure and provide support for at least three subpopulations in Montana. FST values between subpopulations ranged from 0.08 to 0.10 and provide evidence for male-biased dispersal. The high degree of population substructure and low levels of gene flow contrast results from wolverine population genetic studies in less fragmented landscapes of Alaska and Canada. This study provides additional support for the hypothesis that large carnivore populations of Montana are becoming increasingly fragmented due to human development and disturbance.
Zonal Flows and the Transition to ITG Turbulence: A Dynamical Systems Approach.
NASA Astrophysics Data System (ADS)
Krommes, J. A.; Kolesnikov, R. A.
2004-11-01
Both large-scale gyrokinetic(A. M. Dimits et al., Phys. Plasmas 7), 969 (2000). and reactive(S. Dastgeer et al., Phys. Plasmas 9), 4911 (2002); J. Weiland et al., J. Plasma Fusion Research, 2004 (in press). simulations have shown that zonal flows (ZFs) can suppress the onset of drift-wave turbulence (the ``Dimits shift''). Here the ``simplest'' reactive ITG model (coupled vorticity and pressure fields with 10 degrees of freedom) is considered and its primary and secondary bifurcations are studied both analytically (via construction of center manifolds) and numerically.(For further details, see R. A. Kolesnikov and J. A. Krommes, ``Bifurcation Model of the Transition to ITG turbulence,'' this meeting.) The primary bifurcation describes a burst of turbulence that settles into an equilibrium in which the drift waves are totally suppressed by the zonal flows. That equilibrium is destabilized at the point of secondary bifurcation, which defines the Dimits shift for the model. The relation of this work to tertiary instability(B. N. Rogers et al., Phys. Rev. Lett. 85), 5336 (2000). and modulational-instability analysis^2,3 is discussed.
Modelling Cavitating Flows using an Eulerian-Lagrangian Approach and a Nucleation Model
NASA Astrophysics Data System (ADS)
Ma, Jingsen; Hsiao, Chao-Tsung; Chahine, Georges L.
2015-12-01
An Eulerian/Lagrangian multi-scale two-phase flow model is developed to simulate the various types of cavitation including bubble, sheet, and tip vortex cavitation. Sheet cavitation inception, unsteady breakup, and cloud shedding on a hydrofoil are used as an example here. No assumptions are needed on mass transfer between phases; instead, the method tracks bubble nuclei, which are in the bulk of the liquid and those generated by nucleation from solid boundaries and this is- sufficient to accurately capture the sheet dynamics. The multi-scale model includes a micro-scale model for tracking the bubbles, a macro-scale model for describing large cavity dynamics and a transition scheme to bridge the micro and macro scales. Nuclei are treated as flow singularities until they grow into large bubbles, which eventually merge to form a large scale discretised sheet cavity. The sheet performs large scale oscillations with a periodic reentrant jet forming under the sheet cavity, traveling upstream, and breaking the cavity. This results in bubble cloud formation and in high pressure peaks as the broken pockets shrink and collapse while travelling downstream. The results for a NACA0015 foil are in good agreement with the experimental data.